We had another poster on here recently who feels it is her duty to fall into the StepMom role (mother) b/c the actual mom is a piece of work. Feel free to search for her thread (it was in the last month).

Its giving her nothing but grief. Both her AND the daughter.

Listen to Vash, she's the expert on this subject.

Good luck. Blended families are a challenge at best and hell at worst. Vash is one of the few examples I know of someone who managed it successfully.