Stepmotherhood

Where to start. Ok so my hubby has a 12 yr old daughter and we never get to see her because her mom won't let her come spend time over here because her new boyfriend doesn't like my husband. Any way we have to wait a few more years before she can go before the judge and say she wants to come live with us. She is miserable with her mom but we can't do a whole lot until she's old enough to appear in front of a judge. I would appreciate any advice I can get. We don't have any kids together yet and I would like to be the best step mom I could be to her. I know mom and step mom have different boundaries. I already love her like my own I just don't know how to be a step mom.