All right,

Let us at first, hope fast full recovery for yours' Mum ,,,,,,,,,,,,,,,,the period of pain seems very long!!!!!since that she didnt asked for a help!!

Any how:
Is she an obese women ?
may be suspected to being have varicose veins!!
may be suspected to being have ischemic claudications? in case if she havent neurologic problems??
What was the nature of her job?? [just in case]

All the above suggestions may be not accurate? as its difficult to diagnose via internet? Your mother needs to see a proper specialized physician soonly!!

Hope these would help!

Good luck