The not-to-be-discussed mystery medical condition? I would bet it’s hemorrhoids. She would NEVER admit to those because embarrassing plus there’s so much responsibility she would have to own up to. Obesity, absolutely. All that weight pushing down on the delicate veins surrounding her rectum, something’s got to give. She does nothing but sit all day and night, another contributing factor. High fiber diet to keep her bowel output smooth and regular? Har-dee-har-har on that. Constipation as a feature because then she doesn’t have to sit on the (likely uncomfortable for her) toilet for long enough to poop every day, just every few days. Downside is horrendous, though, because when constipated material gets around to exiting, well, it’s gonna take a bunch of time and hurt and pressure on the rectal area. Which, surprise, leads to hemorrhoids. Oh, by the way, which can then bleed and burst. Which also, by the way, can make her think she’s suddenly gotten her period after not having it for a long time when blood shows up in the vicinity of her undercarriage.
Further problem would be that she’s too fat to take advantage of things like a sitz bath as is commonly recommended. It’s credible she can’t wipe herself except maybe with a Bottom Buddy or similar device, so witch hazel pads or Preparation H are right out.