Payback is a witch

Cathy didn't know what happened to her as she found herself more tired and weaker second by second. As the young nurse at home felt her knees not enought strong anymore to wear her own weight, she could see that, in front of her, the old Linda seemed to feel better and better at the contrary. Cathy even gasped as she could see the 90 YO lady becoming clearly younger as, herself, was growing older. Then, she understood :
"What... what did you do to me ?!" Cathy asked with a feeble voice.
- I know everything Cathy : you stole my money when I was asleep. But too bad for you, I woke up just in time the last week and saw you. I don't know how long you did this. But I will make you pay with this Stealing Youth spell. Don't mess with a witch, young girl ! Linda said, as she was now a 28 YO blond woman.
-Please ! Give me back my youth ! I will give you back all your money !" pleaded 90 YO Cathy.
- I'm too old to care as much as you about money. I prefer your youth"
Cathy felt in despair as Linda took off her old dress, admiring her beauty and her youth rediscovered. Then, she knelt down to be at the same level as Cathy.
"But don't worry ! I'll give your youth back... one day. Just the time for me to have some fun".
Linda planned to spend just only one week-end in her youthful appearence but preferred to stay vague. After all, she wanted to give a lesson to Cathy. And the look her nurse gave her when she let her on the house to "get out and get laid" was priceless.