XW is not your friend, XW does not have to talk with you !! It’s up to DH to put effort into his daughter

Step away from the ex-wife. This is your DH issue to deal with. Best to just let him.

If your DH doesn't care enough to be upset, then I don' t think there is anything you can do about it. His XW is right, she doesn't have to talk to you. She probably resents your intrusion especially since your DH seems fine with the current arrangement.

" She refuses to talk to me and says that if the father has a problem that he can call her. Not only do I find it disrespectful and rude to me , What’s even more hurtful is that my husband refuses to acknowledge or say anything."

This is as it should be. It is your DH who has a child with BM, not you. She doesn't have to give you the time of day. And frankly, it would bother me as a BM to have SM contacting me over issues and concerns about my daughter. You are not co-parents. Your own Dh, the father of the child, does not care enough to communicate with BM nor to keep up on things involving his daughter, so why should BM play parent with you?

That's not trying to be mean to you. You may very well be a very caring concerned SM who really wants the child to be a part of your home. I would imagine the mother has been done this route with your DH before. You are wife #3 and the girl is 18. BM is likely use to Dad slacking on his end . Maybe it was SM#1 too that had to try and do all the co-parenting and communicating also. Maybe Mom, as her daughter is now 18 , feels if Dad was going to be involved Dad would have done so instead of having SM do it all for him.

This is an age of school online portals where parents can view report cards, grades and school calendars while sitting at home or using their phones to access the info at any time from anywhere.

Kudos to you for wanting this young lady to feel you and Dad and the younger siblings and step-siblings would like to be a part of the older girl's life and activities. But you can't do this for Dad. It is him that needs to make the effort.

Leave the mother alone. If the girl is 18 the girl is quite old enough to pick up the phone and say 'hey, Dad, I have Senior night at school, would you and SM like to come?'. When this young lady graduates next May/June she will be considered an adult. It will be entirely up to Dad and his daughter whether they will have any relationship or not and what it will be like. You don't say how old the other child of DH's is from his ex-wife and first marriage, but I will assume probably around HS age also?

Does Dad have visitations with his older children? Does he communicate with the older kids when they come? At some point Dad has to take responsibility for his own relationship (or lack of one) with these kids. You can't do it for him. No matter how loving and caring you might be, this is Dad's job as the children's parents.

If DH is angry you don't do his job of communicating , you sit that man right down and you remind him who the father and the parent is. All this is between BM and Dad when kids are younger and between Dad and his kids when they get older.

Focus on your own children and your child with DH.