I would absolutely talk to her about it. If you email make sure you save a copy of the one you send and any responses. I wouldn't wear her out with a report on every push and shove but a bite is serious. Esp, at almost 4. They should have pretty good language skills. In my experience kids bit to avoid or obtain something. (for the most part). Even in play biting is serious.
Don't be to hard on your self, I have had biting occur literally right next to me! It happens in the blink of an eye! I always keep a very close eye on the one that bit after an incident. I would reassure the mom that you are keeping a very close eye on the child in order to assure it wont happen again.
Deb

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