I guess her wrist would swell a bit because of the heat but it should be back to normal afterwards. If she is happy with the fit and feels comfortable, she should choose the 16. Otherwise she might be better off if she chose the 17.
As for color and diamonds... that is a tough decision

I love both YG and RG so I'd say that it depends on her skin tone and what suits her better. Personally, I prefer the love without diamonds; there are much more beautiful diamond braclets available. The classic screw design is what appeals most to me. But having that said, everyone is different!