probably by ditching some ribs, or by doing something akin to what this woman does.
I doubt she's tight lacing, though - you have to wear that corset pretty much 24/7 (well, once you've trained your body to take that kind of compression, and with the exception of showering), and she's not wearing one in any of these pictures. Yeah, the figure stays for some time after you take it off, but that's just not striking me as what's going on here.
I'm going to go with rib surgery. Removal itself is extremely rare, but having the ribs actually
crushed isn't unheard of, either. But if she's willing to do all that other stuff, I don't see why she wouldn't do that.
(Being someone who ends up counselling a lot of trans women through gender dysphoria, I've learned a bit about what can and can't be done in reducing your waist/rib cage.
)
But those eyes. Jesus. What is going on with those eyes?