I vote for "vent, forgive as best you can, and move on." It's probably a no-win situation at this point, and even the best case scenario doesn't do anything to mitigate the damage (?) done to your DD socially with her peers.
Mitigate this with your DD, of course. OF COURSE. Oh, and don't ever FORGET that this happened. Because this person has just shown you a glimpse of what she really thinks about kids like your DD. I've found that those glimpses are instructive and ignored at one's peril.
I've also found this kind of statement to be the most harmful of all, actually, when it comes to DD and her self-esteem/imposter syndrome, etc. Our kids seem to KNOW the significance, too-- they know that the person saying it is subtly denigrating their ability and competence.
Since you didn't hear it firsthand, you don't really know how it was stated-- or, in fact, IF it was stated so brazenly.
Talk to your DD once you cool off a bit-- find out what actually came out of the teacher's mouth, find out how much it bothered your DD, and then decide how much it would be worth (and cost) to pursue it with the teacher.
If the teacher is someone that will be part of your lives, it MIGHT be worth it to bring it up casually at some point as "something that my DD found oddly hurtful." But I really wouldn't make a huge deal of it.
