Welcome to Health Care Magic..
I read your query and it seems that repeated exposure to Salmonella typhi
is responsible for your mothers typhoid posite results..
I sugest her to be on antibiotics even after symptoms of fever is off , I would recommend Ciprofloxacin
as antibiotic of choice which has good effect in treatment of typhoid fever
Ty21a vaccine is administered intramuscularly and it is recommended to take a booster shot after five years.
Typhoid is a completely avoidable condition, avoid locally prepared foods and water to keep the disease away . (Pakaged or boiled water is safest) .
Hands should be clean before cooking or eating .
Do not eat fruits and raw vegetables that have been precut.
Provide plenty of water to your mother as it prevent the dehydration
that results from a prolonged fever
and weakness. She may need to receive fluids through a vein in your arm (intravenously) if severely dehydrated.
Hope this information is helpful .
Thanks & Take Care .