Also, she isn't around you as much because she is more comfortable with her biological mom.
You becoming a new mother to a man who already had that experience with a woman, is a tremendous thing for that kid.
Now she has to deal with another person, this permanent decision from her dad, while growing up in two different homes.
Did anyone talk to her about a new sibling or did it all just kinda happen, and y'all thought about living arrangements after? If that's what happened, you guys weren't thinking about her. You were focusing on yourselves.
I don't know what happened between her father and that lady, but you can say that you have a good relationship with somebody, and not understand what kind of emotional stuff she had to watch her mom go through at the hands of her dad.
((Yes, I understand SD may have complex feelings about being pushed out but that's for her dad to discuss with her at length so she understands the constraints of reality.))
^ her feelings on the matter are unprocessed at the time, it can be perceived as trauma to her since the child already has previously existing trauma after the separation of her parents.
This was a decision made without her involvement, if dad flunked one relationship he was supposed to work on/work out, he shouldn't be procreating with more women and putting his daughter through that emotional stress.