This is tricky and long-term whateveryoudecide may be harmful if there are other conditions that none of us is aware of. IOW, see a doctor, and follow the prescriptions and advice if any are forthcoming.

Low BP may be due to heart failure, valve failure, arrythmia, poor electrolyte balance, too little sodium (although that usually makes a person feel quite ill), dehydration. The thing is...............................................which is it? Then, what should be done for your mum? Will that do something worse? How will you predict it? With what information that is reproducible and veridical?

The long and the short of it is that this needs a physician's assessment and advice....and follow-up. We can make suggestions, but always with the caveat that we don't know what comorbidities your mum is dealing with, her history, her age, her body weight, any endocrine issues,...the list goes on. We can't advise you legally or ethically due to this lack of knowledge.