I imagine it's a matter of how serious it is to you, how distracting, and whether you're willing to believe your therapist or not.

You won't find a perfect one out there, they all have issues/flaws/quirks, so.... is this quirk worth trading for another? It's extremely likely you can find a competent therapist who does not have this particular (nervous-sounding) habit, basically, a therapist who does not fidget, but you'd have to start over and hope they didn't have a worse trait.

I can't really advise you, except to weigh how significant this is to you given all the other factors. I can see how it'd be irritating, and how it'd seem a bit strange your T would not stop if she realized how bothersome it was to you.