Cindy:  You are right that a low blood sugar without symptoms can be
normal.  If she has no symptoms at the time her blood sugars are low, then
the low blood sugar is probably of no consequence, and then if the weight
loss is unexplained by nutritional issues, she probably needs a work-up
for other causes of her weight loss, as you said.
However, there is one condition with hypoglycemia that *is* serious and
needs to be ruled out, if this woman has *fasting* hypoglycemia (as
opposed to reactive hypoglycemia, i.e. after intake of food).  If her
sugars are very low in the fasting state, she may have a rare tumor known
as an insulinoma (an insulin-producing tumor).
If her low blood sugars are symptomatic and occur after food intake
(reactive hypoglycemia), this may be an early symptom of diabetes.  There
is considerable debate as to whether the entity known as reactive
hypoglycemia exists as a separate condition, but some women who suffer
symptoms of low blood sugar after eating do appear to improve with the
kind of diet that Pamela recommended.
Hope this helps, Alicia Dermer, MD, IBCLC.