Weighted Vests for Teenage Girls?

Hi, I was just wondering if weighted vests are healthy for early teenage girls and if so how much weight is adequate. I would really like to know as it is my sister's BDAY and she's been asking for a weighted vest forever so I thought I should get it for her, but I'm not sure how much weight I should get her, I was thinking around 22 lbs max, adjustable so it could go lower. As always any advice is welcome. Lots of love to the FB fam!