Why is this girl so obsessed with my weight and what I eat?

I'm helping with a project and this girl has taken it upon herself to monitor my diet and workouts.

It started innocently when she came into the bathroom once and I was changing out of my workout clothes. She asked me "Wow it's so early, are you coming from the gym?", then later asked me about my weird looking drink which was only veggies.

I don't drink/eat any sugar because it's bad for me and I crash and get hives all over my neck and chest but obviously it's also to take care of my physique. She kept making little comments and jabs but today she annoyed me so much.

People were taking orders for Starbucks as a way to treat us. When I was asked what I wanted I simply responded "I'm actually good but thank you so much", they simply nodded like it wasn't an issue and all of a sudden I here very loudy "Um she doesn't eat any of that because she doesn't want to be fat like us", ummm.. I have NEVER made any comments towards anyone's body or weight, I simply don't give a fuck.

The guy asking for the order was like "Nah quit that stuff again", Again??? I didn't even know she had been making those types of comments about me to other people. She cackled and said to me "No, you'd be embarrassed to get a bloated stomach or get "fat" right?" She used quotations and a mocking voice when she said fat.

I told her what I eat or don't eat is none of her business and she should focus on herself instead of policing when I come from the gym or go to it. She's also the girl who takes a look at my food and asks me to come on try a chip.

She just grinned and now that I came into my spot I see a Starbucks drink with a post it saying "Gaining a pound won't kill you" with a winky face.

One of the girls is saying to me that she actually sent pictures of me (from my private account might I add and we're not friends so I don't know how she got them) saying I photoshop. It's just ridiculous, I've done nothing to this girl, I mind my own business but she's fixated on what I eat, when I workout, and apparently is saying I'm on Ozempic and I'm just so annoyed I don't know what to do.

I take really good care of my health physically and mental wise so why is it anyone's business what I do or don't do?