I work in a studio so I see all the gifts that come in for the instructors. It is really up to you, gifts are not expected but very much appreciated. I would suggest something consumable. If you know she likes coffee bring a Starbucks with you next lesson with something to eat. Instructors are always hungry. We makes pots and pots of coffee in our studio. Wine is good. Flowers are also appreciated. They stay in the studio where the instructor can see them all day. Something that can be shared, like chocolates is good because some instructors get more than others and this way they can share the wealth. I have never seen cash given ever and since instructors are professionals, they would be insulted. A gift card is better. Stay away from personal stuff like jewelry, clothes etc.