Weekly is too much and so are large rats. A medium once every two weeks, give or take a few days, is plenty for a snake that size and for the rest of her life. Most ball pythons are overfed. And I would definitely recommend getting perches or branches that can be fixed in or are heavy enough she can't move them. They enjoy climbing and is very good for their muscles but they do tend to knock things over. Of course you don't have to offer things to climb if you don't think you'll be able to safely, but it would be good for her