Firstly I've seen photos of gorgeous people I know which make them look much less attractive before. Honestly. People might be beautiful but still have one angle, among hundreds, that is particularly unflattering, and which happened to be the one captured in that one photo which gets put up on social media. It's very unlikely that that's what you look like all the time.
And also you could consider the possibility that the photo isn't that bad, it just happens to tap into your current insecurities. Maybe in a month you'll start to notice nice details about it. In any case, you sound beautifully groomed and people really notice that. Please don't let it spoil your memories of the night - I'm sure you looked fab, and other people who were there will remember you looking fab. Why does your previous opinion, where you felt great for the first time in ages, suddenly get discounted by a single photo? You gotta trust your own opinion more.
Secondly, do ask her to delete if it bothers you, that's fine. People have put bad photos of me up before, I don't really mind tbh, but if it did bother me I'd have no compunctions about getting them to take it down.
People just don't think, honestly, I'm sure she won't be doing this to show you up or anything. She'll be thinking in her head, Wilbur is so gorgeous that I'm sure she has tons of self confidence and it won't matter a bit that there's one slightly dodge photo of her on the internet, as anyone who knows her knows that she's tons more attractive than this! Even her comment kind of points to this - she is acknowledging that you can look much better, that you have a 'best look'. I'm sure she'd be vv surprised to hear that you have insecurities about this, whereas if, in her eyes, you were a less attractive person, she'd probably think twice about putting up less flattering photos of you (assuming that she is normally a caring friend). I don't know, I guess when it's a case of hurt feelings, it's much more often the case that people are thoughtless and/or can't possibly imagine that it would have an impact on people's self-perception than that they're actively being nasty.
Also, fat old women are often v. sexy. Just sayin. :) Ageism does you no favours.