Tw for emetophobia(very strongly encourage you to not look if this is a problem for anyone reading this seeing as it's mentioned a lot), death + poison So I'm gonna approach this as accidental mithridatism because that makes sense for her. Mithridatism is the practice of regularly dosing yourself with poison in increasing non lethal quantities which tends to have very not awesome effects like vomiting and just absolutely wrecking your immune system What this leads to is either death, because you messed up the dose or poison, or drug resistance. Luckily for Mari, even if she's unhappy with it, she got resistance! Drug resistance (or Antimicrobial resistance (or or AMR)) is what happens when your body gets used to drugs due to misuse, overuse, or underuse and stops being affected by them or more specifically it appears because of the mutations that take place spontaneously in any group of growing microorganisms or cells, whether exposed to medications or not. So while she doesn't have to fear most attempts at poisoning her, she's screwed the second she gets greencough or any similar diseases seeing as she wouldn't be able to use most common herbs to treat it as she'd be immune to them and will most likely die because of it. Even if the medic does manage to treat whatever may ail her, it'll take far more herbs than the average cat and could very easily accidentally kill her thanks to the high dose. Going back to the aforementioned vomit thing, the amount of herbs she'd be consuming all at once to reach such a high tolerance + the bodily backlash would eventually just straight up eradicate her gag reflex/ability to vomit, which would once again not be great for her in a situation where she ate something poisonous since a) yarrow + most of the other vomit inducing herbs don't work for her and b) nobody would be able to force her to vomit.
Sources: - World Health Organization - Cleveland Clinic - NIH