Thanks for your responses. It's a frightening situation to be in.
To reaffirm, the doctor she saw was a GP (general practice), the first line of treatment in the UK. It was here she was refused medication or referral and instead persuaded to get away from me. I have no idea what was said during this appointment, but I did overhear the telephone conversation to this doctor prior to this when she explained along the lines of "my partner feels I am this...". Seemingly this was the trigger and the reason she was called in to the surgery for a face to face! It seems strange practice that the doctor was more interested in her relationship than assessing her mood.
I understand that a number on here are convinced she's a manipulative abuser, but I also want to make clear you've only got my side on this. I'm a bright enough guy and I'm normally fairly effective at reading people, and I'm simply not convinced she is intentionally abusive. When she's in a positive upswing / on a good day she's kind, loving, proud to be with me and generally considerate. When she's on a downswing / on a bad day I'm often convinced she doesn't love me, and feeds off resentment. I can feel loved and supported one day, to hated and resented the next. Things got so bad that this became highly cyclical to the point 50% of days were bad days!
Since the breakup, she has understood and accepted she cannot behave as she has regarding my wearing of diaps. She has also seemed far more understanding of my wider sexuality, preferences and needs. I've made quite clear that she either has me as I am, or she doesn't have me at all. I'm not changing for anyone, it would be insulting to both sides of the relationship. What's surprising to me is that for close to a year she has been uncomfortable about my wearing, has said all sorts of contradictory things and in general not been supportive, but now she's prepared to drop her whole issue with me and them, providing I understand some clear sexual boundaries that I thought were already established (when wet, most intimacy is off the cards except for PIV).
Today she spoke to an actual counsellor, and they have undermined the doctor's advice by suggesting she does a) need to resume antidepressants (she was taking them during university some time before we met) and b) it's likely her behaviour is a result of depression / anxiety rather than a personality disorder. However, they are prepared to refer her to a psychiatrist.
I have asked during the past few days now that we are on much better terms if she can explain to me why she has been the way she has. Her explanation of this is that when angry or not thinking clearly, she has said inappropriate things that didn't come out as she intended them to. To me, this seems really odd. How can someone say controlling and manipulative things as a result of their depression / mood unless there is intent to affect someones actions?