Just tell her. Buy her deoderant and show her how to use it. Simple!

Here are some ideas:

She is NOT to wear anything more than once then it goes straight to the laundry room.

Buy her talc powder or some feminine smelling powder that she would love.

Buy her deo and tell her to wear it EVERY day (even if she doesn't think she needs it).

She MUST change her sheets twice a week, every week.

Buy Downy Infusions fabric softner (long lasting) or Gain detergent and fabric softner. They both smell good, are very strong and long lasting.

Is it because she is dirty (doesn't bathe, doesn't wash clothes, doesn't wear deoderant)? Or does she do all of those things and still smells? and how old is she, is she heavy?? I watched a Mystery Diagnosis once about a woman who had some rare disorder that caused her to smell bad.. she went through years of torment in high school etc about her bad BO before they figured out what was wrong with her.

Probably a stretch... but just sayin

If you are trying to spare her feelongs, try sitting down with both girls and explaining hygene. Say that now that they are both older that their body care needs to change accordingly.

Lay out exactly how often they are to be showering
Buy them each a few kinds of deoderant (stick, aerosaul, gel) and ask them to try then and let you know which they like best.
Have them strip their beds reguarly.
Make sure to mention that just because they can't smell it, doesn't mean others can't.

Yes, it will be entirely for sd's benefit but she shouldn't get defensive if your dd is included in the talk too.

I dunno. I had the same problem that age. For like 2 days.

Then my mom told me I stank, I was going to wear deodorant even if she had to get my dad to hold me down and apply it, and I was going to shower everyday, no questions asked.

It worked.

My approach is the same as DeeDee's- my 2 older ones would occasionally have stinky pitts and I would tell them point blank that they stunk and DO NOT forget to wear deodorant again. (they were all tought at age 7 how to properly wash body/hair)My DD13, the youngest, is a total dirty slob but she never ever stinks. She just doesn't have the "stinky" gene.

I just flat out don't let any of the kids leave the house unless they can pass a general hygene inspection. I don't even care if it makes us late and I HATE being late. My ds has long hair which he gets to keep if he washes it and keeps it brushed-which he does. Brushes his teeth and showers daily. The ss15 is Horrible! He comes over on friday night and by sunday morning for church it is a Battle to get him in the shower! If we don't mention it and make him he wont even change his clothes all weekend! Summer is over so the public chlorine bath at the pool is no longer an option. The ss are also not circumsised to they get this REALLY funky sour smell to them if they don't shower! Both the ss hate to brush their teeth and hair and have brought lice into our house twice now! Same thing with the sheets on the bed, every morning they have to be put back on the mattress as they always pull them off and throw them on the floor.
I guess it could be worse with if they were girls with the pad thing..I don't even want to imagine that mess!
I feel for you!

Have her Dad be in charge of it from now on. He needs to check her clothes and make her shower and change clothes and sheets. He needs to tell her how nasty the period-soaked pants are and make her put her sanitary items in the trash appropriately.

I would still spray air freshener and demand nasty stuff be out of the room for your own daughter's well being. How horrible it must be to be forced to live in a room full of blood-soaked smelly nasty BO and butt smell all the time.