Thanks for your question on Health Care Magic.
I can understand your concern.
She is having
hypotension which is recovered by fluid and salt intake.
This is suggestive of
dehydration, lack of oral intake of fluid in her.
Other causes for hypotension are infection and heart diseases.
So better to get done
complete blood count (CBC) for infection and ecg, 2d echo for heart diseases.
If all these reports are normal then no need to worry for infection or heart diseases.
Lack of oral intake of fluid is the likely cause in her case.
So ask her to drink plenty of fluids orally and keep herself hydrated. She can take lemon water with salt once daily.
Don't worry, she will be alright.
Hope I have solved your query. I will be happy to help you further. Wishing good health to your mother. Thanks.