S.C.
Of course it is always appropriate to give or say thank you, but that does not always happen. Did you like the teacher this year? Did your child have a good year? If so, then this teacher deserves a thank you gift just like you gave her. And don't worry about whether you get a thank you or not- that's not really what the spirit of giving it about anyway.
Things slip peoples' minds. It's the end of the year, very busy. Maybe she did give a thank you to your child who neglected to get it home. Maybe the gifts got mixed up and she doesn't know who gave her what and she is embarassed because she can't figure it out(that has happened to me!)Who knows?
If you really are concerned that she did not get the present, then just ask. I'm sure she would say, "Oh, yes, thank you so much! The gift cards and candle are lovely!"