A woman I know (under 30 yrs of age) has been experiencing hair loss for a couple of years now at the center of the head, down. It started mostly when she started working a stressful job, which -- along with her other symptoms -- leads me to believe there's an adrenal issue that is impacting the thyroid, leading to hair loss.

It sounds to me more like she is dealing with "male pattern baldness" (MPB), which can affect women as well.  Stress in general can lead to hair loss by nutritional deficiencies, autoimmune alopecia and thyroid suppression, but the hair would fall out all over.  Poisoning from some metals or chemotherapy also make the hair fall out all over.  Infections would cause the hair to fall out in patches.  Top of the head is usually from dihydrotestosterone (DHT) responsible for MPB.

However, she recently went to a lab that told her that her hair follicles are dead.

Again, death of the hair follicles is usually from DHT.

It's possible there is a conflict of interest there -- they do sell hair products, including "natural" hair --

Possibly, but if the hair follicles are dead then their products are not going to help the hair to grow back.

but, assuming they are right, is there ANY way to re-grow hair in those areas?

No, once the hair follicles are dead then that is it.  They cannot be brought back to life.  If the follicles are dead then you will not see any signs of hair, not even fuzz.  If there is some fuzz left then the hair follicles are still alive.

She nonetheless wants to try fixing her thyroid and adrenals to prevent any possible further loss, and to alleviate her other symptoms.

She still needs to confirm what the likely cause is.