Hi
I feel for you - my DD is now 12 years old and has suffered from constipation since she was a baby. She has been under various NHS hospital consultants for most of her life and she's suffered from daily faecal soiling and megarectum (stretched bowel) as a result. We tried absolutely everything they suggested....high fibre diets, prune juice, pears, increased fluid intake, loo breaks 20 mins after eating, bowel transit time tests, lactulose, senokot and Movicol. For the last 4 -5 years she's been taking 4 Movicol sachets and 25 ml of senokot daily just to keep things moving.
Anyway, I would suggest that you do as a previous poster suggested and go see a nutritionist or naturopath as soon as possible and get your daughter tested for food intolerances.
I'd always been a bit suspicious / cynical about these intolerance blood tests, but after years of absolutely no change under conventional medicine (and a DD about to enter her teens where the potential social consequences of faecal soiling are just devastating), I decided we had to try another approach and took her to see a naturopath this spring.
We discovered she is intolerant to cow's milk and wheat. We cut those out of her diet (pretty easy now with so many great products on the market) and she started taking various probiotics and digestive enzymes. Eight months later, she is virtually off Movicol (just half a sachet a day), totally off the senokot, ultrasounds show her bowel has returned to normal size and she has stopped soiling totally.
It has been such a long and difficult road, but I cannot describe the difference it has made to her life.
Your DD may be in a totally different (& less extreme) situation, but I wish to God I'd thought about checking this out sooner and feel so cross with myself for blindly trusting conventional medicine for so many years even though I could see her condition was not improving. I think the NHS is amazing, but sadly, I think the doctors just aim to treat the constipation, rather than looking for the underlying reason behind it.
In any event, it might be worth a punt. Severe constipation in children seems to be incredibly prevalent in the UK but notoriously difficult to 'treat', but in eight short months, my DD's life has totally changed. If sharing this can help anyone else avoid the years of anguish we've been through, then hurrah for that!