Simple words pack a great deal of punch. Fear, grace, trust - each speaks volumes with one syllable. And then there is "nice".
"Have a nice day", "what a nice guy", "buy her something nice". We're way past cliche here. Though there are surely people who would relish being called nice, my guess is most of them would prefer being called gracious or kind or enjoyable. Don't each of those alternatives conjure more specific behaviors than nice?
A good friend of many years is the most decent and even tempered man I've ever met; my wife is a person with a rock-solid core of integrity, generosity and non-smarmy charm; the new neighbor I just met strikes me as straightforward. Are these all euphemisms for nice? Am I splitting hairs? Didn't I start out saying simple words pack a great deal of punch? Perhaps, probably, yes. But tell me your preference. Being described as nice (or... it's two syllable equivalent - "pleasant")? Being described more specifically? Or...if someone can't come up with something better than nice, not described at all?
Enjoy your day and be sure to get her something thoughtful.