helping to raise a step child

Has anyone else on here become a step mom to your SO's children? I have been in my step daughters life since she was 7 months old. She is now 3 and going through that sassy stage.. where no and but are always her response when asked to do something. She's at our house every weekend and when she is it's mostly just me and her. Because dad works nights and sleeps during the day some nights when we have her.