UGGWomen's Classic Short II Chestnut Ankle-High Suede Boot - 9M

My wife wears a 7 1/2. Which size would be ideal for her?

Size says b(m) What does that mean?

Are these for men? the description says women's classic short ii boot. but on the size choices it's got a m after the size. can you tell me what's go

Do they run big or small ???