Low testosterone can make you really tired, too. Ask any perimenopausal woman.
However, that's usually associated with declining testosterone (as well as other hormones) as we age. So, if you do any research on your own, that's likely going to be the context of the information you find.
Testosterone does fluctuate during the various stages of the menstrual cycle, so if you don't have that piece of info, the numbers won't make complete sense. If it were me, I'd want to know my full range over my cycle.
The higher her testosterone gets during one phase of the cycle, the worse symptoms may be if it drops really low (it's the drastic change that we notice).
Based on my personal experience (47 year old female), a level of 6 would be extremely low, and expected in someone who is in menopause/has stopped ovulating. A level of 13 would be more normal in someone my age (still ovulating, but things are starting to shut down).
Testosterone levels in women are typically highest in the late teens and early 20s.
Testosterone is really important for women, and not just as a "sex hormone". It's important for bone density and mood/cognitive function.
Just as a side note, it may be difficult to find a doctor who even thinks this is a problem. It's only been the last couple of years that the medical field has started taking hormone therapy for older women seriously again. And most doctors are still stuck on the old way of thinking (ie, hormones cause cancer - which is not true). The buzz right now is there is no "FDA approved" treatment for low testosterone in women. Well, that's just because they haven't bothered to approve a treatment in the right dose (there are FDA approved treatments for men).
You might be able to find an OB/GYN who specializes in this, or an endocrinologist who specializes in fertility. You also might get help from a knowledgeable female urologist.
My best advice is to take this as seriously as if a doctor told you your son has low testosterone, and find a doctor who does the same.