Step mom to step mom it is hard at times with older girls. They truly feel like you are taking time that their dad should be spending with them. They also feels more for their mom. My little girl I think battles with whether she is being a traitor to her mom by coming to me.
My best advice is find things to include her in. Also, encourage your husband to once and a while get some one on one time with her. Lately I have been including my little girl in cooking, and different art projects. But remember it also has to be something she likes to do. These things will give you a chance to bond. Always give your heart to her and treat her like your own. Try to feel for how hard this must be on him. Good luck...
you have to understand that from where she stands you're taking her mom's place and you're also taking her father from her so she's gonna give you a hard time ... from what you wrote you're still better than most cases i've seen at least she's not acting out (skipping school, drinking, smoking, drugs ... )
i think you should give it some time and if you're nice to her she will open her heart to you :)
good luck :)
How long have you known her? It might be a matter of more time.