For anyone curious, google image search up Charlotte Mckinney, she's a model that's 5'7 and 145lbs, with roughly similar (though definitely smaller) breast sizes to the FMC here.
Though I'm not shocked that a mangaka has zero clue of what reasonable weights are for women. Like, if you look up pictures of women around that height and weight, you get tons of "after" pictures of someone who just lost a bunch of weight and now looks very fit. Most of the before pics are around 180-200lbs or so, and look like how FMC is drawn.