First rule of thumb that it took me YEARS to learn...don't surprise her with a knife...GET HER INPUT.
I learned this after buying her half a dozen CRKT's, Spyderco, Benchmade, and Kershaws, and the more I thought she would like them, the more she actually hated them. Then of course the one knife I never thought she'd care for (a Blackie Collins "Buddy System" she immediately commandeered and hasn't returned it after three years of daily carry on her keyring.
That having been said...my wifes VERY favorite folder that she refuses to carry most of the time cause she loves it and frets over it so much is a Benchmade 940
The folder that is TRULY her EDC is a steel handled Spyderco Delica. She hasn't left the house without it since I gave it to her a few months ago.
Another one of her favorite knives is an MOD Scorpion neck knife that she immediately confiscated on site late December.
She also got a Benchmade 335 "Big Spender" for Christmas that she carries around her office alot (Political Correctness factor and all)
good luck to ya!