systolic Blood pressure of 100 is not too much low it may be due to appetite changes or she is having some anti hypertensive medicines. If she is taking skip a doze or to by regularly checking blood pressure if it is above 140 take medicines otherwise skip. If she is not taking any medicines it may be due to less intake. Give him some oral rehydration solutions (O.R.S) and also an egg daily. For thyroid she should have Thyroid function tests
if it is hypofunctioning it may be due to hypothyroidism
for which she had to take Thyroxine
tablets daily as advised by your physician.
If the oral intake is decreased she should have intravenous fluids to restore blood volume.
I hope I am sucessful in solving your query If u have further you can ask me
Get well soon
Dr. Azhar Sattar