I'll need to run out and get some Cointreau when she's gone. When she finds out it will probably make things worse.
Smart. I think that the keys to a good margarita are good triple sec and lime juice (rather than sour mix or anything pre-made). Better to spend your money on the Cointreau, and economize back a bit on the tequila, than to buy high end tequila and cheap accompaniments.
Like vodka, it's better to save the high end stuff for drinking it neat.