Hi Jess,
I wouldn't get hung up on some nominal temperature that the manufacturer claims!
The key thing for camping in the snow comfortably is the amount of insultation you have underneath. So in summer conditions I am comfortable camping in the snow in what is basically just a nylon bag (it was a 150gm of down summer sleeping bag but is now very old and has lost all its down), as long as I have a good mat and lie on top of my jacket and overpants too. Even in a very warm bag you will get cold if the insulation below you is not right.
Winter conditions are of course more serious because of the lower air temperature. I have a standard (NZ) tramping bag 750gm of down for those trips.
A bag that is too warm won't be that practical for lots of trips and you'll sweat so much you ruin it quickly. Women seem to sleep colder than men though, so would depend on how cold you sleep.
I would focus on a good quality brand, 4 season bag, some kind of surface that can take a bit of damp and a really good sleeping mat.
My 2c worth.
Richie