Wheelchair for our 12 year old daughter

Our daughter has just turned 12 and has been diagnosed with hypermobility, chronic pain and PoTs. The NHS will not help with a wheelchair for her as she can mobilise for a few minutes. She cannot walk though more than a few minutes and less than 50 metres. She has to stop, sit down or lie down or she will faint. She is dizzy on standing and has to hold on to something when she stands before attempting to walk. She sometimes faints on standing. She can no longer attend school and the school

has given her a AVI so she can still keep up with lessons. The NHS will not prescribe any medication due to her age and her referral to cardiology was refused. She cannot walk though no longer go for outings with her grandparents or family as she cannot walk. We need a wheelchair so she can come with us and have a life again. She is already 5ft 10 so needs an adult size wheelchair and one she can power as she wouldn’t be able to push herself due to the fatigue.