Of the two choices, my personal opinion is that for concealed carry, the 642 with its shrouded hammer (you're gonna shoot a J-frame in a self-defense situation in DA anyway and its no-snag draw from a holster, pocket or purse) is a much better option than the 637, but my preference would be the 442 (black finish over whatever S&W puts on the 642 that chips and peels off). Someone mentioned the Bodyguards, which does provide the option of cocking the hammer.
I will say that over the past couple of years I've encountered several women ranging from twenty-somethings to AARP-eligible who say they prefer revolvers due to the simplicity of operation. Yet, as others note -- a lightweight J-frame is not super-fun to shoot. A bit easier, though, with standard-pressure 148 gr WCs or 158 gr LSWCs over the lightweight fast movers (125 gr +P JHPs).
Even though I'm turning into a bit of a Colt revolver fan (the new Cobra is excellent as is the 3" King Cobra), maybe the Kimber K6 would be an option. A bit more weight, 6 rounds over 5, excellent sights, and arguably a better trigger than current production J-frames..
Off-topic, the wife has chosen for her current carry piece a SIG P-365 with the frame-mounted safety while one of the daughters goes with a SIG P-228 (she says she shoots bigger handguns better and doesn't mind the size and weight).