I'd start with how SHE feels about it. Forget about what everyone else feels. If it becomes even a hint of a power struggle, the whole family loses, in many ways.

And I must interject that you may have very fond feelings for your BF's daughter, but you're not her parent. The quickest way to lose your man is to insert yourself between he and his daughter (that is, if he's a good dad!). It doesn't have to be overt; even the most subtle advocacy or position-taking can be misconstrued, especially by children. Make sure you have earned the trust and respect of both of them before you make decisions for her without her input, or champion her cause with her dad.

27 years in a divorced/remarried/child-of-divorce/step-everyone family have taught me a few hard lessons. Children are the most vulnerable victims.

Karen