I wouldn't really worry until she's lost enough weight to look visibly skinny. I'm talking you can see the backbone, there's less weight in the back half of the body, and she's more shaped like a triangle than a circle. I wouldn't put a precise number on it, because it's hard to say exactly when a snake hits that point. Obviously losing half their weight is an issue, but is 1/4 the weight an issue? It really depends on the snake.

So in your case, 3 months doesn't sound like much to be worried about, and as others have suggested, try waiting until you get home and offering live again. Personally, I'd get her eating again, and then at that point try switching back to F/T while you still have access to live rats just in case.

Good luck!

-Jen