Aw I really feel for your DD.
When Dsis and I were around 10 and 9 respectively, dad remarried. She seemed nice enough. We were very polite and well behaved kids (had a disciplinarian dad who wouldn't allow bad manners or behaviour) so never had any issues with her.
She had two kids (3 and 6) that lived with her ex. We would all get together at weekends and all was fine.
When DF and his DW moved house again when I was 11 and DSis, 12, DF's contact lessened and we never went to the new house. Eventually DF took us but only when our step mum was out at work and only for an hour or so. It turns out, SM had banned DF from seeing us and he was meeting us secretly. There was no reason other than she didn't want DSis and I in their lives. Her kids had a bedroom each at their house for their contact weekends and DSis and I weren't even allowed in.
I still can't to this day believe that DF went along with that for so long!
It all came to a head when I accidentally left my homework there. I needed it and would never have left it intentionally. He phoned up screaming at us, saying I'd done it on purpose trying to cause trouble between him and his wife. I was too upset to speak so DSis took the phone and for the first time in our lives, stood up to him and shouted at him to "FUCK OFF!" If he wouldn't own up to seeing his own daughters then he could fuck off and leave us alone.
I don't know what happened at his house after but we did eventually go back to visits out in the open. (Still didn't get a room of our own though)
Dad is with a nice lady now but as I'm an adult with my own family contact isn't really an issue. Whether any woman likes it or not I wouldn't let my dad stop speaking to me.
OP, if your DD is unable to speak to her dad, it wouldn't hurt for you to say something to him. It doesn't matter what age your children are, you are still parents together and your kids involve both of you. See if you can get his number from a relative, call him up and ask him what the hell is going on. Your DD has a Dad problem. The SM is the cause but only because DF is going along with it. Get him told.