Can other factors besides AGA cause miniaturization? Sluggish thyroid/low ferritin - can either cause it, too? Is it reversible?

I recommend seeking out a good Functional or Integrative Medicine physician that can and will work with you at identification and treatment of the root causes of your condition. 
Once they are under control you will have greater success working with a hair specialist to regain what hair you have lost. The hair you have will likely recover to a condition you haven't seen in a long time. 
Wishing you the best outcome.
Warmly,
Arbella Sarkis, MD 

I never like giving advice to women for treating hair loss, as there are so many possible causes of female loss and every woman responds differently to the various therapies available. With men, the great majority of the time it is just genetics.
Rogaine (minoxidil) is the most popular hair loss medication used by women around the world (and the only FDA approved treatment for women)… but you need one doctor who is willing to work with you. Seek out a caring dermatologist and work with your hair loss problem.