The rudeness is completely unacceptable, you're right to not tolerate that.
However, you do need to find a way to figure out WHY she feels like this. Pps have suggested numerous possibilities.
I'd like to add to the voices of those that ED are NOT just evidenced by an unhealthy weight (in either direction, I personally think it's woefully under recognised in the overweight that their issues are rooted in mental health causes - and I'm a fatty myself!)
Any weight loss might not happen immediately or at all. I know people who've suffered from bulimia who were a "healthy" weight throughout.
It's the emotional relationship with food that defines if there's a disorder.
She may also be afraid of losing you/her stepdad if they're close to conditions related to being overweight and is clumsily expressing that.
My (very slim but eats loads - high metabolism due to disability) dd was talking to me the other day about her friend who is very overweight. Dd was saying she "couldn't understand" her friend not overtly wanting to do something about it yet clearly unhappy with her appearance.
At one point she said something like "I'm never going to let myself get fat" I reminded her that at her age I was actually slimmer than her, told her I'd had similar thoughts, was "determined" never to get fat "like my mum" (my mum was only about a size 14 and has always been fit with loads of stamina)
I asked her how she'd feel if she suddenly had to massively reduce how much she ate of her favourite foods, up her exercise (she has to do certain ones/a certain amount as physio for her condition and HATES it) and couldn't wear the clothes she likes. Hopefully she'll have more empathy for her friend now.
I also reminded her that in our family the women ARE very slim UNTIL about a year after first baby they start gaining (I have my own theories on why). It can creep up on you, it doesn't happen overnight.
Your dds attitude to both food AND people she perceives as "greedy" DOES need to be seriously addressed.
My dd in commenting on her friend at NO POINT devalued her based on her weight, she's concerned for her friends happiness and health.
Tbh I would be concerned I'd gone wrong as a parent if she were seeing people as "lesser" because of their weight/eating habits.
That's not a nice attitude to have at all.