My everyday carry is a LCR that I've put about 200 rounds through. And I just acquired a 360 (the scandium frame Airweight) from a fellow forum member. I haven't shot the 360 yet, but I can offer these observations.
Trigger: The LCR is DAO and the double action trigger is superior to that of the S&W. It's lighter and more linear and doesn't stack. For someone who doesn't spend a lot of time practicing, it's the ideal "point and shoot" weapon. The S&W trigger does stage better, however, if you're taking your time and trying to make an aimed shot.
Fit and finish: The S&W wins. However, I will say the finish both inside and out on the LCR's cylinder is as good as or better than I've seen on any revolver. The chambers are mirror smooth which aids in extraction and cleaning.
Lockup: The LCR wins. The cylinder on the LCR locks up a tad tighter than on the 360.
I think the LCR's grip design really aids in reducing felt recoil. I've fired some old Treasury Dept loads in mine and it wasn't bad at all.
The LCR at 13.5 oz is lighter than any of the std S&W alloy/steel J-Frames. If she likes the 642 and just wants a lighter version of it, she'll have to step up to the much more expensive 340PD. That's around 12 oz, but it's double the price of the LCR.