I had this with a bullying colleague almost 20 years ago.
It wasn't the only issue but it's what it started with as the office we were in had a tradition of bacon butties on a fri afternoon from the nearby greasy spoon. All I did was ask for a fried egg one instead as I'm veggie (free range eggs too I'd checked)
She then kept trying to "catch me out" "isn't that belt leather?" No "those sweets you're eating have gelatine in" no they don't I checked "but you eat eggs" yes vegetarians eat eggs.
From there it escalated, she then found out certain things about me (this was pre sm people barely had internet so how the hell she found these out I dread to think!) like the religion I'd been raised in, that I was of Irish descent etc and started making some really nasty sectarian comments, then she got really personal as she somehow found out then husband and I were considering ttc and made some comments about I'd need to become more attractive & "less uptight" first so he'd want to have sex!
She was very careful not to make the worst comments in front of anyone else.
It all got me very low I reported the issues to our boss (who was her drinking buddy and encouraged "banter" as its now called) who handled it very poorly and to my shame I didn't take it higher and instead quit just to get away!
I moved to a different part of the organisation well away from her and that boss but she then took it too far with another victim, was unaware that boss's boss was nearby and overheard and ended up sacked!
Boss was disciplined too because as it turned out she was doing this to most colleagues and the boss had received numerous complaints which had been basically not dealt with. How the boss didn't get sacked I don't know.
Horrible time and I wish I'd stood up for myself better but that can be bloody hard to do.
Even after I left there were some odd incidents which suggest she was following/watching me (she lived in next street too), at first I thought I was being paranoid but my then husband and closest friend also noticed she seemed to just always be around and in places she basically had no reason to be in - all very weird!
If I came across someone like that now I hope I would have the strength and sense to make an official complaint and to recognise them for the nasty bullying gits they are!
Definitely consider having a word but I would say to protect yourself keep it calm, assertive and unapologetic but public!
Maybe
"I would appreciate it if you don't make unwarranted and unsolicited comments on my life/dietary choices. I don't comment on other peoples. It's unnecessarily critical" other mners may have better suggestions but I would avoid being passive or in any way apologetic, you've done nothing wrong.
If she does it again, you can basically repeat that but add if she doesn't quit you'll have no choice but to report the issue.
Then if she still continues after you've made it clear and others know this too then you're in a stronger position to take it further.
Fun though the suggestions are I wouldn't stoop to her level as you then lose any leverage. If she's the only one that's said anything out of order you're in a better position to complain about her if it becomes necessary. If you say anything out of turn to her she can then use that against you.
"She’s the type who can dish out but she will not take it." Totally agree. The second you step out of line she'll use it against you.
The fat shaming crap pisses me off, I'm fat I know why and I know it's my own fault. My dd is very very slim, largely to do with her disability, which is invisible, yet she often gets appallingly derogatory comments about her figure, mainly from strangers and all over things like sm there's nonsense like "real women have curves" (I'll lay odds this woman shares this kind of bullshit!)
No! Real women have a wide variety of different body shapes and sizes THAT is what should be acknowledged/celebrated. Being either end of the spectrum because of eating too much or not enough is unhealthy of course, but shaming people for their figures is known to be counterproductive.