Step mothers.

Lately I've been reading a lot of post about step mothers and how they feel about their step kids. I just have one question... If you were in a situation where you're the step mother, would you still get involved in their lives and what they do, ALTHOUGH their biological mother is in the picture? I have a friend who lives with her boyfriend and he has his kids 50% of the time. Meaning, they live with him part time. My friend feels like she's not really involved in those kids lives because their mother is in the picture and she takes care of everything that has to do with her kids. Plus her boyfriends kids don't see her as a mom, they just see her as an adult and the person their dad is living with... Not to mention, my friend is pregnant ...They're all old enough to know what's going and I think a major problem is that they think she's not such an adult bc she's young compare to their dad... So How involved would you be in a situation like that?