first of all i assume she is under medical care; if not she should seek it immediately as that is dangerously low.
there could are other possible reasons but one cause of low blood pressure is a serious condition called hypothyroid, or low thyroid. other symptoms include poor memory, fatigue, low body temperature, low sex drive, difficult menstrual periods, hair loss loss of the outer third of the eyebrows, dry skin, brittle nails, puffiness in the face, and weight gain or sometimes weight loss. hypothyroid is more common in women than men.
though there are other causes, a common diagnosis is hashimoto's autoimmune thyroiditis. the cause of that is uncertain, though a few studies point to a possible link to chronic systemic infection]. some think there is evidence for a genetic reason.
some researchers believe that exposure to flouride, mercury, aluminum, and other elements harms the thyroid and/or inhibits absorption of essential minerals. essential mineral deficiency could be a factor but should be approached with caution as supplementation may also cause problems, especially iodine with hashimoto's.
some hypothyroid sufferers report increased symptoms with certain foods, cooked and especially raw. cruciferous vegetables, soy products, some oils commonly used for cooking, stone fruits, most grains (rice and wheat may be okay), and many root vegetables seem to lower thyroid activity in some. there is disagreement among researchers and medical professionals about this and many other aspects of thyroid disease.
advanced low thyroid can cause serious health conditions. if you think you have low thyroid, seek a good doctor who is flexible and willing to do some investigating. many patients with symptoms of low thyroid report being diagnosed as being euthyroid (not high or low) based on superficial testing, and their symptoms attributed to depression or other causes of fatigue. many patient groups advocate doing more complex testing. in addition there are many kinds of treatment and many patients also report ongoing symptoms in spite of treatment, as well as issues with changes in formulation, prescription, and availability of medication around the world.