take her to a physiotherapist if you have a local one,you will have to pay but at the end of the day it ts worth it,i had a back problem for months,went into hospital for tests came out the same,couldnt find out what it was,i made an appointment with a physio and he knew straight away,i had three months ultra sound treatment and was fine,that man made me sane again,you could see a physio through your doctor but it could take ages, and if your mum is in so much pain it would be better to sort it asp,if its a muscle problem, like mine it wont show up on scans or xrays