On my mountain bikes, I like longer crankarms than on my road bikes, so I use 175s on my mountain bikes. I ride with more of a masher style on my mountain bike (by necessity), so the extra leverage is good. For reference, I'm 5'4" with long legs (never measured, but all of my pants are at least 32" long) and I ride a small Niner Jet9 and a small Salsa El Mariachi. Like your daughter, women's specific rarely works for me because of my long arms and legs, and I end up feeling too cramped.
As for stem, have you talked to your shop? They might have some cheap loaners that you could use to dial in fit before spending money on something good.