Adopting a snake and learning

Had a friend who for unknown reasons had give up his ball python. I offered her a home and couldn't be happier! I was unsure at first but now I'm glad. But still learning. She was eating every week for the first month but now refuses food for weeks at a time with no health or activity changes. She's supposedly 2 yrs old and about 3ft long. Is it normal for diet to change like this? Not sure if she's really female that's just what the pet store to!d her original owner. She only sheds every 2-3 weeks. Could she be full grown?