Hi thanks for your question.
Fall in blood pressure can cause nausea
and vomitting,but what matters is,how much is fall in blood pressure level ?what was her previous blood pressure level ?or what is her usuall blood pressure level ?.These are few important points in history which you have not mentioned and are necessary for labelling blood pressure as cause for her nausea and vomitting or need for informing a Doctor.Blood pressure level of 98/44 is not that much low which will cause nausea and vomitting.The other reason for nausea and vomitting could be gastritis
that is inflammation of stomach due to variety of causes like infection by H Pylori,spicy food,cigrette smoking
and alcohol.Blood pressure is usually normal in mitral value prolapse and her heart rate
is normal as in old age heart rate usually remains on lower side.Finally at this age a neoplastic lesion in stomach is to be ruled out as cause of nausea and vomitting.I would suggest you to consult her Doctor who will be able to examine her to find out cause of nausea and vomiiting and low blood pressure.
Hope this answers your question.