My question is, if she's happy with the P232 why switch? I don't see anything in your post indicating that the P232 isn't working for her at 18 ounces, but that it's not a Walther.
If weight is the primary consideration, and the P232's 18 ounces is just right, then stick with the P232 would be my advice. It's as solid a weapon as you're going to find.
That's exactly what I would have thought. It might be best for her to stick with what she has. In any case I don't think the OP will find what he's (she's) looking for in the Walther World, at least in terms of weight.
For reference, here are some real-world “on my kitchen scales” weights of the two nearest Walther contenders:
PPS Classic, steel sights, large backstrap, unloaded (PPS M2 is not significantly different in weight):
with 6-round magazine: 612g
with 7-round mag.: 615g
with 8-round mag.: 621g
P99c AS, steel sights, large backstrap, unloaded:
with flush 10-round magazine: 621g
with finger-extension 10-round mag.: 623g
with 15-round PPQ/P99 mag. including plastic extension sleeve: 650g
There are, of course, lighter pistols with the Walther name on them but the quality of materials/workmanship/reliability would not be comparable with the above two, nor with the SIG Sauer P232.
Balor