Wow I sure can identify with you, Sloppyjo. I have always felt the need to please everyone, and I feel guilty if I feel I'm falling short. Now I am trying to not be so hard on myself and just go with the flow of things. If I can please someone then that's great, but not at the expense of making myself stressed out or neglectful of other things that are important to me.
As far as your stepdaughter, I believe you should support her as much as you can. My son has told me on more than one occasion that just because he's older doesn't mean he doesn't need me. I'm sure your stepdaughter feels the same. I wish you the best, and your family too!
Sujin