I feel like you’re slightly missing why St. Rose would work to blister her face. At a young age she obtained permission from her confessor to take a vow of virginity. Then, as she was getting older, men started taking note of her because of her beauty. As a way to discourage men from looking at her she cut her hair and rubbed her face with pepper to cause blemishes. She didn’t do it as a self-mortification for something she had done, but instead did it to prevent others from being tempted by her and potentially tempting her from her vow to the Lord.
At least, that’s what I learned as I studied her life as she is my Confimation saint. I could see why you would get upset about the crown of thorns she wore that pierced her head, the sever fasting, the little sleep, and other things. However, the face thing puzzles me since it was in response to men looking at her and she didn’t desire marriage even though her family did.