I am at my wits end. Really. Please help.
I have a bright, intelligent, confident and funny 4y3m old DD. She has just started school.
At home and when out with us or at friends houses, she takes herself to the toilet whenever she needs to go with no problems and no prompting.
Going back in time a bit to provide a bit of background...at nursery at around 3.5yo, she started to wet herself most days she went there (only went 2 days per week). She had been dry before that. I got the impression she would try and hold on for the whole day without going to the loo, inevitably by the end of the day she would be wet. She always refused point blank to discuss anything about this with me. I always approached her in a calm, understanding way, not an angry way. We never got to the bottom of this behaviour and hoped that a long break from nursery over the summer and the transition to school might break the pattern.
So now she is at school. This is week 3. The first 2 weeks she attended for the mornings only and I was really hopeful that as she had no accidents we had made a breakthrough. She has really settled well at school and has been delighted to go every day so far. So now we are up to full days in week 3.
Monday she came home smelling strongly of festering wee and her knickers were soaking.
Tuesday as far as I could tell was a good day, no tiddley smell and dry knickers.
Wednesday she was dry. I thought we had cracked it.
Thursday she came home in the school's spare skirt and knickers, hers were soaking wet in her bag. She refused to talk about it. I asked why it happened - she refused to comment.
Today there was a stay and play session at school this afternoon so I went along from 1:30 to 2:45. Soon after I got there, I asked if she had had a wee today - answer was 'no'. So I took her to the loo (all of which were clean and tidy and perfectly pleasant so mucky toilets really isn't a factor). Her knickers were already saturated when I touched them. Sigh. 30 mins later she told me she needed a poo and I asked her to pretend I wasn't there and take herself, but that I would follow her. Which she did and went with no problem. I dread to think what would have happened if I hadn't been there.
DS refuses to discuss it. I took the opportunity to have a quick chat with her teacher as I was in school today. She was really surprised and confirmed that DS has settled in extremely well and seems to love school.
I can feel myself shifting from being sympathetic and understanding (she is only just 4 after all) to feeling really angry and frustrated with her. She is totally in control of her bladder. She chooses for some unknown reason to not go to the toilet, and when her bladder is full quite consciously wets herself and carries on as normal even though her knickers (socks and shoes) are full of wee.
I just can't get through to her. Why would she wet herself when there is a toilet available 10m away?
Does anyone have any similar experiences they could share to keep me sane? Oh and a magic solution to stop her doing this would be great. 
Thanks for reading this far.