My DS has been through a few teeth grinding phases, but generally they've passed after a couple of weeks... The only thing I can suggest is some sort of distraction when you see her do it - maybe offering a rusk or something to chew on?
DS would do it a bit when he was teething... Maybe as Miss E said, when you see her doing it give her something good to chew on. And don't make a fuss/draw attention to it either. We did that to start with and DS thought it was funny and would keep doing it.
there is nothing you can do, she will grow out of it, just dont give her any attention when she does it, it only becomes a concern if they're still grinding when the adult teeth come through
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