Where are you from? In my country, bringing a T a Valentine's Day gift might be very unexpected and easily interpreted as a plain gesture of courtship, which would likely not be accepted. But maybe in your culture you'd give out Valentine's Day cards or small gifts to friends, family, etc, in which case it wouldn't be a problem. All I'm saying is, do consider the context. Don't give her the gift as you would to a potential partner because she will probably not react as you'd want her and you will only get hurt.
If I were you and wanted to give her something, I'd give her a card with my best wishes / thanks to her as a good therapist. A small gift like chocolates or flowers if it's common in your country. If you want to get her jewelry, make sure it's nothing expensive because an ethical therapist would not accept that. Perhaps you could give her a handmade plastic bead bracelet or something else that you made? The more symbolic the better.
Of course, I'm not trying to dictate what you should do. If you want, you can even give her an all-out romantic gift, of course, just please be aware that she's unlikely to accept that kind of attention from a client. I hope you make the best choice for yourself.