Thanks for posting your query.
After reading your mom's symptoms, i feel that the weekness may be due to change in her Blood pressure. Sometimes, when a patient is on medication for blood pressure he/she does not check the B.P on a regular basis, therefore the dosage of medicines may not be ideal after some time.
I would recommend you to ask her to visit your family physician for a general check up. If the blood pressure is not the cause, then your doctor may ask her to get a basic complete blood count
to evaluate her hemoglobin
, iron levels as well. Low iron levels usually result in fatigue
Meanwhile she must have fresh fruits and green leafy vegetables to enhance her body resistance. If required the doctor may change her B.P medication and also ask her to take multivitamins and iron tablets.
Hope she feels better soon.