IMO royals with questionable work histories likely use legitimate medical diagnosis as an excuse to do what they want. Unlike regular people there are no economic consequences to not "working" so this gives the perfect excuse. Basically while I do believe the diagnosis is legitimate, I do think that the restrictions are very likely being over exaggerated because she doesn't care to work unless she has to...or at least I wouldn't be surprised if they were. Simple fact is her official program has never been anything impressive and any "changes" would probably go unnoticed but by putting her diagnosis out there and blaming her health for her light program they can shame anyone who dares to criticize her.
You are right about royals using medical diagnosis as an excuse because of no consequences.
But, regular people also, at least in my country, usually don't have economic consequences. It might depend on your employer.
This is off topic, but:
I had a very stressful experience with a coworker who was ill for three years, never showed up, was diffusely diagnosed with "psychic problems". Once in a while she came to work telling us how exhausted she was, made herself a cup of tea and went off again for months!
Me and my coworkes took up her workload for 3 years and that was a lot and meant awful stress for us. We worked for a public radio and tv station calculating and organizing public events, radio recordings and productions for 5 different musical genres, classical, modern, jazz, historical music and folk music.
If any of us was ill for just a week or two, it caused problems because the job was so specific.
If this woman was diagnosed with a feasable illness such as cancer, or a lung desease or anything serious, we would all have understood and have felt empathy. But we had the impression that she was using us.
It took a very long time to get her fired ( involving the head of personnel department and lawyers and paying her a compensation etc.) I have heard she found another job which wasn't so stressful and obviously no psychological problems in that job.
Why didn't she do this the first time, because our social system permitted it. And who suffered the most, me and my coworkers and the whole bunch of people who were involved and dependent on the outcome of this person not doing her job.