One 20-25 gram adult mouse is plenty for a 300 gram young adult snake, every seven days. I'd keep her on that schedule (not every five days) until she is about 400 grams, then move her to every ten days, one adult mouse, and watch her weight. It is okay at that point for her to gain slowly. If she is still growing rapidly, or getting fat, you can move her feedings out to 14 days.