“Overweight” absolutely is an attack when it’s paired with the poster bragging about how she follows a diet and works out 4 times a week. She’s trying to say: “Look how I do everything right and I’m the best, and how this person is the worst and they’re living with the results that come from doing the wrong things in life.”

The substance of the offending interaction wasn’t even about appearances, she just needed to crowbar it in there.

By the way: something most people are glossing over is that she admits she already knows the HR complaint will amount to nothing because she is friends with the HR person who she’s apparently had discussions badmouthing this coworker, so she knows they feel the same in disliking her. So this company’s Human Resources process is rigged in this instance, and the HR rep is telling the original poster to make nice for the sake of appearances so HR doesn’t look like the sham it is. She’s basically saying: “Obviously I’m not gonna take her seriously. She’s totally the worst. She can go eat a dick. But do me a favor and just apologize so we can pretend I actually did my job after she filed a complaint.” And she can’t even bring herself to do that for the sake of her HR friend.