As finals approached, Clara was exhausted. Between school, witch training, and her part time job she felt like didn't have a spare second to rest. She needed a break and she just found something that could do the trick.
In one of her potion books was the recipe for a youth potion. Not only would it allow her to become any age she wanted, it would also alter reality so no one, her grandmother included, would know the difference.
All of her knowledge and training should remain intact, so when she's ready to get back to normal it should be no problem at all. After carefully brewing the potion, she considered whether she should invite anyone to join her and how young she wanted to get.