I started seeing my therapist in early December (7 years ago) so thought a bit about if I should get her something. Then the next year I thought I should but like you wasn't sure if it was appropriate. Ended up getting her a Slinky, nicely gift wrapped the box. When I gave it to her she said she didn't accept gifts (and I can understand that but not all therapist feel that way) but she did say she wanted to open it just to see what it was.

Well after she saw that is was just a Slinky she did accept it. And just an FYI for everyone a Slinky (metal not plastic) is the best stress reliever out there, the sound it makes as you shift it from one hand to the other works wonders.

So I suggest Slinkys all around (get one for yourself too), they are inexpensive, and with the explanation of why you got them one a very thoughtful gift that won't be considered inappropriate by anyone.