It's a warning to other would-be tamperers. I'd rather lose weight by exercise and eating wisely, painful though it is, than have liposuction. There's not much logic and no morality in my limit-setting, but there are consequences from meddling with nature, and your friend has stumbled on one of them. I don't think you did any harm or caused offence by saying nothing about your friend's plastic surgery. She is still your friend and much the same person underneath.
People usually have plastic surgery for their own benefits.
For reasons known only to your friend she has chosen to 'enhance' her natural features. I think it is up to her to broach the subject of her own body. Help by accepting her for herself. It caused tremors in our relationship at the time. Counselling did not work, but we talked openly and I decided to forgive him.