I was jealous of my nieces and nephews because my stepmother was treating them (her grandchildren) with more leniency than she did me and having fun with them, etc.

I guess the only way to get your own life back is to think of something of your own, an adult something, that you want to do and do that; go to a meeting or class and meet other adults or even a mother/daughter thing where you can meet other parents. She's 6, there's not much real "relationship" going on there :-) They can barely write love letters, LOL (my stepmother saved one of mine from a boy in first grade).