You can switch her more or less immediately. With older snakes sometimes it's wise to wait until summer, when they've got their appetites back. But hatchling ball pythons are pretty much always hungry... it's getting them to figure out HOW to eat the first couple times that can be tricky.
But it sounds like she's got that part down pat.
If she doesn't go for the f/t mouse right away (after you've thawed the mouse and dried it and warmed up its nose a bit with the heat lamp or a blow drier) you might try leading with a tiny live mouse and then offering the f/t as a second helping. At that age, you usually only have to do that once or twice for them to get the idea.