There are a few things I've been told you can do to switch over from a mouse to a rat. I don't know if you've tried any of these methods, but here they are:

1) Try switching to live temporarily. Start with a smaller rat and make sure you monitor the whole time. If you are really uncomfortable switching to live, then perhaps try pre-killed. I don't know if it necessarily has the same effect, but maybe the more consistent body temperature will help?

2) Whether you do live, pre-killed, or F/T, rub mouse scent all over the rat and present it to the snake. You can go to a pet store and ask for bedding from a mouse enclosure and keep the rat in a box with the bedding for a little bit (make sure the bedding isn't infested or anything).

3) Another method I've heard of is called "priming" (Ithink!). What you do is get two prey items, one mouse and one rat, that are about half the size of what you would normall feed (half the size your ball pythons should be eating). Start with the mouse and offer it to your snake. After your snake has eaten it and stretched out some, offer the rat. Once again, sometimes scenting the rat with a mouse smell may help.

If your female is at a good weight and not too young, you can also hold off feeding for a feeding or two until she takes the rat. If she is relatively small though, I wouldn't do that. Also, have you tried just leaving it in the enclosure over night? Hope this helps a bit and good luck get your little girl eating rats soon!