Hello, your assumption that it could well be your lower back which is causing the problem could be right. Having said this; there are a multiple amount of other possibilities.
a) you point out having sustained over the years in a slumped (bad posture) position does not help. It causes many disfunctions of muscles (poor recruitement of some and shortening and hyperactivity of others) and irritation of a lot of joints involved.
b)poor posture can cause easily bulging of discs or irritation of facet joints (joints between vertebraes) or Sacro-Illiac Joint disfunctions
You point out that your mother of 42 needs to see on a regular basis a physio while the problem is not solved. Since you have no diagnose of your mother's problem, I can only guess; possibility a or b or both. Bulging of discs is a good possibility since that seem to have to do with poor quality of discs which can be inherited.
I would if I were you ask for a diagnose of your problem in stead of getting the advice of just self massaging which will not cure the problem but can keep it under control. The physio should be able to put a working diagnose on the problem if he/she can't you better look for a physio who can.
Example; Poor gluts strength can cause tightening of Hamstrings ( a straight leg raise= SLR should easily give some 85 dgrs hipflexion) tight Hams causing a pull on the pelvis downwards forcing you to slump (people who sit a lot can't recruit Gluts and are prone for tightneing hams)Slumping position makes gluts not work and core muscles neither as a result you're prone for a pelvis disfunction, hip disfunction and core stability issues. Therefore you need to know if the hams are tight, if your pelvis is aligned and if the lower back is not forced in a bad position. A booklet "treat your own back" by McKenzie might be of some help to understand your problem but I would not just do the exercises of the booklet without consulting a physio who will put a diagnose on it in stead of racking in money on a weekly basis.
Hope this will help.
Understand that where you feel discomfort does not mean there lies the problem!