My 10 year old has been diagnosed with severe constipation and often poos herself as she doesn't know when she needs to go, she has been given a number of enemas but nothing seems to work, I am very frustrated as I don't know who turn to?

You will need to change her diet.  Caffeinated drinks for example cause dehydration that causes bowels to be void of liquids needed to cause normal elimination.  I also suggest lots of water or Gatorade.  A good idea also is to give fiber pill to regulate bowels.  Cut out candy or sweets.  Serve three meals failed and good whole grain treats.