Pics would help, but fuzzy mice are way too small for a normal 3 month old ball. Most hatchlings right out of the egg can eat larger than fuzzy mice. In fact, don't even bother with mice. Switch to rats. They are more nutritious and making the switch now will be easier than switching an adult mouser. Offer her a rat as big around as the fattest part of her body (roughly 10-15% of her body weight) once every 5 days. After she hits a year old, switch to a 7 day feeding schedule.
Edit: Looks like Lisa beat me to it. You'd be surprised what ball pythons can swallow. It may seem like a lot, but I assure you, it isn't.