I've just started Minoxidil/ Rogaine (women's, 5% foam). Will this help reverse PCOS hair loss? Is shedding normal?

Multimodal treatments are usually necessary for PCOS. The ideal is usually a combination of minoxidil, oral contraceptives, spironolactone and low level laser. Be sure to see your dermatologist or endocrinologist for advice. These treatments aren't appropriate for everyone. Minoxidil helps 30 % of women with genetic hair loss, but not everyone. It helps halt loss and may improve hair density a bit. It can thicken hair a little bit and promote growth of dormant hair. Yes, shedding is common in months 1 and 2. PCOS related thinning usually requires more than 1 treatment for most effective results. I like to add zinc and selenium to my general recommendations as well. 

Razavi et al
studied the effect of receiving
either 200μg selenium daily (n=32) or placebo
(n=32) for 8 weeks. Jamilian et al studied the effect of 220 mg zinc sulfate (containing 50 mg zinc) (n
= 24) or placebo (n = 24) for 8 weeks. Although the short in duration, both studies
showed an improvement in various clinical parameters and improved hair growth. Speak to your dermatologist if these are right for you or not. REFERENCESRazavi M,
Jamilian M, Kashan ZF et al. Selenium supplementation and the effects on
reproductive outcomes, biomarkers of inflammation and oxidative stress in women
with polycystic ovarian syndrome. Horm
Metab Res. 2015 Aug 12.  

Jamilian M,
Foroozanfard F, Bahmani F et al. Effects of zinc sypplementation on endocrine
outcomes in women with polcystic ovarian syndrome: a randomized, double-blind
placebo controlled trial. Biol Trace Elem Res. 2015 Aug 28.  

Some people develop shedding on minoxidil initially which usually reverses in 2-3 months. You must see it through it you want to experiment with the benefits. What minoxidil does, is grows new hair, not reverse miniaturization. Finasteride, reverses miniaturization when it works.