i'm personally not a fan of the "trinity" ring unless it is a princess cut trinity with princess cut chanel set on the sides as well. You ahould ask her to see what her feelings are on princess cuts instead of just round
anyways, instead of asking here on RS, why not go to an actual diamond forum?
RockyTalky; Diamond Jewelry Forum - Compare Diamond Prices, Discussions & Diamond Information
If you do decide to buy online, then PS (Pricescope) will have a lot of recommendations