Wouldn't it be more shitlordy to actually get the size she says she is, then say "Sorry it doesn't fit, but you said you were a medium. We did provide the dimentions of the shirt sizes to all participants before ordering, so it's your responsibility to make sure the numbers match up with the size names."  Or just list the actual numbers, like "32 to 34" instead of "large" so she has to put down her actual size. That would be extra shitlordy! Especially when she gets the wrong size because the last time she measured herself was a few sizes ago, or because the tape measure won't even fit around her gut.