feigning being dyslexic??

I've never done that...
But I do mimic people's handwriting.
I can forge anyone, except my mother's.

It's some subconscious respect that keeps me from it.
I mean, she IS my mother.

As a young bpd sufferer myself I am going to be frank with you. She is faking and she is just loving that she is getting a rise out of you. I would do the same thing to my parents, doing odd things making them think I was sick. I reveled in the attention even if it was bad attention. Paying any attention to it/actually confronting her about it is the stupidest thing you could do at this point. I'd say she is learning to twist and manipulate to get attention and feel validated. This has been so ingrained in me that it is HELL to try and go against it.
Do not pay attention to it, do not talk to her about it, do not say anything to her about her manipulating or creating a coping mechanism.
My mom did exactly what you were doing and it was the wrong thing to do. By paying attention to these little lies and tricks you teach her that her idea work and she will move on to bigger things then writing silly letters. She is most definitely doing it for 'fun'.

Thank you ALittleCrazy

I appreciate your response - I am learning all the time about my daughter's problems, which are certainly very complex and I will take what you have said on board.

Thanks again x