I'm sorry you feel so hurt by all this. And while I appreciate that you are eager to help your husband and try to do what is best for this little girl, she isn't in fact your daughter. She has a mother and a father. I'm concerned that it's you who doesn't want to lose her, rather than her father alone. But she is not yours to lose.
This girl's mother would be awful to prevent her father from seeing her, and I despite women who do that. My fiancé's mothers stopped his father from seeing him for 10 years. It's a disgusting, sickening thing to do.
However, she can decide that you aren't allowed to see this little girl. She says this girl is being verbally abused by you, and even if she isn't, that won't matter to a court ... You have zero rights to this child. Not even grandparents have rights, never mind stepparents. So for your own wellbeing, stop fighting to see this little girl. You won't win.
But, by all means support your husband in his battle for access to his daughter. This is very important, and good for you to support him. But always remember that this isn't your little girl, no matter how much you love her.
Good luck
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