Unfortunately there is no treatment in terms of medication that you can take for low blood pressure.
There is only medication for treatment of high BP
In the short term she needs to be assessed by a Dietician to assess her diet and the improvements that can be made to it to combat the malnutrition
. Malnutrition drops blood pressure. Sometimes to dangerously low levels.
She should sit or stand up slowly to prevent a further sudden decrease in pressure.
She also needs some support, professionally, to help her deal with her emotional issues. Other wise she will be on a Merry-Go-Round.
Until her BP increases to an acceptable level be her friend and help as much as you can. If you can of course.
Once her BP is stablised she needs to continue on with the Dietician until he or she is satisfied there is no more further risk to health.
And continue to seek professional help until she is able to deal with her issues and life on her own.