I absolutely do not mean to defend MM here and the details of her diagnosis defo seem sketchy.. And I am so sorry you've had such a rough time, BUT endo is a really common condition which for some people can be managed with surgery and it may not return as extensively, for others it can flare up a handful of times and then disappear, and for some it can be debilitating and unrelenting.If she really did have endometriosis there is no way she would be able to do a job as stressful as being a creative director of a huge company (albeit I don't think she does that role correctly anyway) plus does she actually know that you can only get diagnosed for endometriosis by surgery?
I work in a very stressful area of healthcare and have colleagues with the condition who live with it and work the same job as me, and I also know someone in my personal life who has it so badly that she has to walk with a stick. Not intending to undermine your experience at all but just noting that for such a common condition, it's important not to assume all those affected are affected to the same degree and 'can't do a job as stressful as being a creative director'