My wife usually carries either an AK47, a Hold Out III, a Code 4 or a Micro Recon I
She struggled with the Hold Out initially (though now it's her usual daily carry), but all of the others she was able to use straight out of the box.
It's true that the Tri Ad takes some getting used to. It requires a slightly different approach. I find a lot of people use the side of their thumb to try and disengage the lock, it's much easier using the tip of your thumb and pushing straight down.
Give it a try and let me know how you get on.
Thank you for choosing Cold Steel, I hope that your girlfriend likes her new knife