Are you sure they will match it? Most of the price matching deals specifically exclude BF sales.
From BB:
"Exclusions apply including, but not limited to, Competitors' service prices, special daily or hourly sales, and items for sale Thanksgiving Day through the Monday after Thanksgiving.
See the list of Designated Major Online Retailers and full details."
My wife got the 38mm because the 42mm looked way too big on her wrist. And, the 38mm looks way too small on my wrist, even though they both measure the same size.

I think it is more about what size she is used to wearing. (big or small watch faces)
TxWatch