They’re plus-size underwear. Put them on a plus-size model. The standard “we’re gonna show you a size 2 but trust us, they come in 3x too!” thing is bad enough, but this time they actually bothered to get a larger size of the product and then put it on a thin woman anyway for some reason.
This does nothing to demonstrate the cut or fit of the underwear i.e. what anyone shopping for clothes online needs to know before buying them. You’ve given plus-size people no information about your plus-size product – thus rendering your entire listing pretty much useless and making people take a shot in the dark – all because you don’t want to show a fat person in underwear.
If I’m buying plus-size underwear, it’s most likely because they are for me and I am a large person. Or possibly that I’m buying them as a gift. But if I’m choosing to buy underwear for another person, I probably have a relationship with that person that involves seeing them in said underwear. It’s not like I haven’t seen fat before. The fact that some people have more flesh is not offensive to me.
Stop marketing fat people clothing toward skinny people.
Showing how your product looks on the bodies that are going to be wearing it is more important than protecting the delicate sensibilities of judgmental fatphobes.