I perform weekly 50% changes on my tanks. That is probably too much on fry living in a 10gal. Maybe a 20% change once a week would be better. Just make sure that the water that you add is close to the same temp. and properly conditioned. Did your friend say how many times the fish bred before she started removing their fry? Was it a one-time thing? If they ate their first batch they would probably learn not to do the same thing again. A lot of fish eat their first and second batches but they usually stop after that. Your fish may not eat their fry if given the chance to care for them again. When they spawn again, leave some for them to rear on their own. If they learn not to eat their young, you will be able to keep them with the parents far longer. This will be better for the fish, their fry, and you.