I also would have to go for the 1.826 because it is a great stone overall. I do think 1.9 range stones are a good opportunity, however, I just can't handle the clarity in the magnified photo. I'm just a VS person in general, but there are some cleaner looking SI1's, too.
You'd have to know whether she would love the slight extra size over having a clean, VS stone. It' part mental and part visual!