Here's my knowledge
Look at her head for her. The previous poster is right that a Doctor is needed for a positive diagnosis, but you can probably figure it out yourself. Women don't need Propecia or Rogaine 5% because they respond much better to Rogaine 2% than men respond to the first two combined. In women, follicles are miniturized but not killed, so their numbers remain and Minoxidil 2% works great. However, let's first diagnose her. Surgery or chemo or birth can temporarily stress the body into hair loss that regrows in 6 months. Look at her balding pattern. If it is roundish and mostly in the front (not hairline) and center of her head, it could be genetic. Next look her scalp. If the hairs look thinner than the rest, without irritation, it is probably genetic. If they just fell out, it is probably some physical stress. If you see redness around the hair follicle, it could be an auto-immune attack on the follicle, known as alopecia aerta or something like that. A few blood tests are still a good idea even if you think you know what it is.