I'm guessing that she is an adult child of your husband?
If so, try not to worry about how she is going to be. It is difficult, I Know, but at some point you do have to let go, and let God take care. I have had to do that with my Own child. They are remarkably equipped to handle things on their own if we can find the courage and strength to let them.
I realize it's even tougher with steps.
The above is looking at it from a parents point of view
This is looking at from the child's point of view. She may be conflicted by having to choose one parent over the other. Which place she will be living at and who would feel the least hurt by her not being there. There are too many emotions to deal with and the first survival instinct is to bury ones head in the sand. 'If I'm not acknowledging or helping, maybe this won't come to pass.'
I do feel for you and wish I had some concrete advice.
All I can do is support YOU in whatever happens.
