I'm new to munching, but why doesn't she break her own leg or something similar?
Munching is less about actually being sick, and more about the attention, care (whether from medical professionals, family, friends, or total strangers), and sympathy they receive for being perceived as sick. This is also why they tend to favor invisible, chronic illnesses without a true fix. Breaking a leg is visible, yes, but it is also a concrete pathology with a defined solution and a limited timeframe. Also, surprisingly slightly less crucially (because they absolutely would milk a broken leg for all it's worth), a broken bone is real pain, real discomfort, and real disability, and that's.... Inconvenient. It really would interfere in their daily life, and to be actually disabled is often not the real goal (although it does seem to be heavily fetishized and accepted as a "happy accident" sort of thing by munchies).
Munchies exist at an intersection of many different pathologies: personality disorders, histrionics, attention-seeking, narcissism, fetishism, and a deeply external locus of control. That is why they're so wild in their claims and pathetic in their whining.
Munchausens cannot be cured. Like Borderline Personality Disorder, it is a set of psychologically-compelled behaviors that can be managed (although almost never is) through awareness of the person experiencing it, and a significant amount of self control. This is antithetical to Munchausens perpetrators of all stripes, because self control and external locuses of control inherently do not mix.
There's also a not-insignificant level of opiate addiction present in the Munchie community, which helps compel attention-seeking behavior.