I have been raising my stepdaughter practically since she was born. She is 3 1/2 and her biological mother has not seen her in over a year and half. Recently me and her father have divorced and his mom has temporary custody of her. How do I get custody or adopt her?

You will not be able to. You may have been able to adopt child while still married to the father, if the bio mother gave her permission. But after divorced, sorry, no, you have no legal rights to child.

I doubt if the father allows it, or the grandparents, and they have the legal standing. Not to mention the bio mother. Sorry, I know you miss the child you have raised since she was so young.