We have 3 bedrooms on our main floor, and we turned part of our basement into a 4th bedroom.  Before DD1.5 was born, SD8 and SD6, who are with us half the time, had their own rooms.  We gave SD8 the option of her own room in the basement or sharing with SD6 once the baby came,  and she chose the basement.  There was no way my bio, who is with us full time, wasn't going to have her own room.  For the first 6 months or so that SD8 had her basement room, she used her room during the day but slept with SD6 at night.  Now she's quite happy in her very private basement bedroom; her only complaint is she doesn't have a bathroom down there. Too bad; I wish I had a master bath but I'm still sharing with everyone else.

FWIW, at the beginning DH didn't like the idea of his kids giving up a bedroom, but he quickly realized there wasn't another alternative.  Our room was barely big enough to fit DD's pack and play (and that blocked access to our closet). There was no way a crib would fit.  It also didn't make sense to put the baby in with his school age kids - if anyone was going to share it had to be them. 

We have a 5 bedroom house and 4 boys. One just moved out and I'll keep his room until he's done with college and I know he's settled. Everyone else has their own rooms. But when our house was being built the step son and my youngest had to share a room. It was a nightmare. So I definitely understand your frustration. If she's never there and probably won't be there much longer, just keep things the way they are. She could sleep in that room if she wanted to. 

I've said it many times before: if you want SKs to act like a member of the household versus a guest, then you have to treat them like a member of the household. Household members get dedicated bedroom space.

Now, that doesn't mean a bedroom sits empty 50-90% of the time. The room could be multifunctional - serves as a home office, craft room, guest bedroom, or play room when SK isn't there. The room could be shared with a full-time kid (a trundle bed, bunk beds, or a murphy bed that could also be used for sleepovers). No matter how the room is set up when the SK isn't there, when they are there, they should have privacy (like any other household member) and some amount of personalization and storage space. 

OP, I think you're doing it right. I have definitely seen others post, though, who complain that their SK treats their home like a hotel but the SK sleeps on a couch, or on an air mattress in someone's bedroom with no personal space or touches. They get treated like a guest and then the SP is floored that the kid acts like a guest. It's one thing when a kid excludes themselves. It's another when they're excluded by their parent and SP just because they don't live there full-time (like they have a choice in the matter). 

The situations all can be different depending on a lot of factors.

I do think a stepkid should have a space that is their own.. but it doesn't have to be their own room per se... but it should have some semblance of privacy.. or at the least be a shared room with another child.

i could see asking one of your daughters to have a trundle in her room to share her room for the rare visitation.. it it is only 2% of the time.. that isn't a huge imposition.. but if you have another space in your home that can be private for her.. that can be an option.

4 bedroom house i have my 2 daughters full time (they don't see their dad). And dh's daughter is only here EOWE. Everyone has their own rooms

Our first home was a 3/2.  My DW was the CP so SS was aways with us and part of our home.  With the exception of his SpermLand visitations.  Even while is SpermLand his room remained his room.  Our 3rd BR was the guest room/study.

Our second home was a 6/3.5.  Still only the 3 of us at least until my DW gained guardianship of my SIL/her younger sister.  Even adding SIL did not cause a space issue.

Our next 3 homes were a 2/2 apartment, a 3/2 apartment, and a 3/2.5 town home with a 3rd floor game room that was our overflow guest sleeping room or where SS slept when either set of his GPs were visiting (My ILs or my parents).

Our final family home prior to SS launching was a 4/2.5 so again we had no space issues.  SS had his room.

Even our maybe "retirement home" is SS's home though it is a 2/2.5 with a study.   

My parents always made their kids welcome and gave us clarity that their home was our home even though it is not the home we grew up in.  My parent's home is the extended Rags clan home.  It is a 6/4 so there is plenty of room for everyone to have some privacy though all 4 of the GKs (SS-28, Niece-27, Nephew-24, Nephew-19) usually stay in one bedroom with two trundle beds and stay up late talking, laughing, etc.....  Now that my niece has married that dynamic will likely change but..... maybe not.  They are all very close and her DH is a really great guy who blends extremely well with the rest of the clan.

I have long been firmly on team resident kids get priorty of bedrooms.   I am also a long time member of team visiting kids need to be integrated into the family.  The blend to these two perspectives is that visiting kids should have a bed which certainly can be a trundle bed in a half/step sibs room, a trundle in a guest room/study, a Murphy bed in a study, etc.....

We have 5 bedrooms and 4 kids. SS's room is the guest room. He is only there 6 weeks a year TOPS. Before we bought our house BS15 would share with SS16 when he visited. BS had a futon in his room, which worked for his friends or as a couch when SS wasn't there.

I don't think kids that don't live there full time need their own rooms. I often thought my ex was crazy for insisting my kids have their own room when they lived across the country. They were really there for a few breaks and summer. I would have made them share, if it was me. 

3 kids and 3 bedroom house. The 2 skids are same sex and close in age. They share a room on wknds now and bio has his own room. DH kicked up a stink at the time arguing why his kids had to share, I asked where he wanted to our bio and he couldn't answer because there was no other room. Skids also argued but in the end they sucked it up and now they both love sharing atleast until the house is made bigger so everyone can hav their own room. 

2 bedroom townhouse, the boys share there room they are 15 and 8 we have a trundel bed rooms tiny but thats all we have 

We haven't had an issue on the number of rooms, but more "location" and how they were being used. When SD11 was living with us full-time she had a bedroom and a seperate playroom. 1. We changed to 50/50 custody 2. She outgrew "toys" and only played on electronics. 

During COVID I changed it to a workout room. SD said she wasa okay with it. Now she pouts from time to time even though she didn't use it. I told her she is more than welcome to workout in there if she wants to, just make sure to put the equipment back. She's too lazy for that though. 

When i was pregnant with DS we were deciding on a nursery. Our master is on the main level, so I figured the bedroom directly above us would be most suited. DH and I argued over this. He said SD11 "needs to be closer to the bathroom because teen girls spend a lot of time in there, right?" Absolutely not I said. And I gave my reasons. 

1. His room is closest to the laundry room. Babies have lots of laundry that I will be doing. YOU do the laundry and then we will talk. 

2. SD barely showers and you're saying she needs to be close to the bathroom? Yeah right. He will be more successful potty training if he doesn't have to run across the house in the middle of the night. 

3. SD complained that his room was "bigger" but never understood that if it's EMPTY it will give that appearance. Literally had to get out the tape measure for her. 

Point being... it's exhausting when deciding rooms isn't viewed as "fair". Fair doesn't always mean equal. Different kids have different needs and that is something blended families have to take into consideration too.