We have a history.
I have a regular who knows how I feel about thank you cards, and he always brings me one or two that are blank because I *always* use them. Then again, I am known by a bunch of my clients for making myself available to them when they need to talk, in person or over the phone. It's hard to not care for people who take the time to care for you.
Little things like a Victorias Secret or Amazon gift card are always appreciated, but if you're looking for advice on what to get for a k-girl,
I would have to say ask her.
Explain that it is a token of your appreciation that she is making herself available to you. Tell her that it could be anything from socks to her favorite food.
If she says that no gift is needed or required, pick out a cute postcard* & give her a little extra on the top.
You are definitely not alone in this feeling, & while we always like chocolates & jewelry, we usually prefer to get them ourselves so they fit our own style.
*(It can be hard for us to keep all of the thank you cards, and having something that is easy to hang or put in a picture frame is much appreciated, & easier to explain to guests at home.)