Next chapter we'll see if Kamoi's Appendix is a Wingorgan or a cockblock.
stomach ulcer is my guess. builds from stress, so would be very fitting for her situation
This has been disproven, most ulcers are caused by bacteria.
While there are a very small number people with genetically weak stomach linings, stomach ulcers are not caused by stress but caused by external factors: Most commonly, bacteria infection with the second most common cause being NSAID (ibuprofen, naproxen (alleve) over-use.
Side quibble: stress will often degrade your body's ability to heal from injury. so it is possible if you have a bacterial infection in your stomach lining that being stressed may result in your immune system being degraded and allowing it to develop into an ulcer, but that is not the primary cause
They wouldn't usually be felt until stomach acidity rose - which it might do in response to steess.
Treatment for ulcers is antibiotics to kill the bacteria and acid suppressors until the ulcer heals. Once healed, there is no need to continue to the acid suppressors.
Of course the question is if the author knows this...
tl;dr: Your body would be very poorly adapted indeed if it wasn't able to avoid being dissolved by its own digestive fluids and cope with the pH of bile normally. I'm calling appendix.