Hi, I would contact the school (or school district) she attended to see if they have a record of their third grade teachers in 1976. The teacher is likely retired by now, but that's where I'd start my search, and having a list of names may jar your daughter's memory.
You might also try contacting some of your daughter's classmates from third grade to see if any of them recall the teacher's name. I've connected with several classmates from the 1970s through Facebook (Classmates.com is another site that may be able to help).
Good luck -- I hope you're able to track down the teacher's name for your daughter.