Just my $.02 after reading this thread:
With my DD4, if something happens just once, she continually remembers it as if it happened again and again. For instance, when my MIL was putting her in the car one day (about a year ago), she accidentally hit DD's head. Now, she won't go in the car with MIL, without crying or warning her grandmother not to hurt her again.
DD is also just starting to differentiate between what happened yesterday with what happened a week or month ago. For the longest time, she kept thinking we went on our cruise, "yesterday" or that Santa came "yesterday."
So, while a 2 yo may not be overtly manipulative, there may be some gaps in understanding. So, if Miss xxx accidentally poked her arm whild your DD was sitting on the chair, it may have had enough of an impact to keep her thinking about it and making a much bigger deal of it in her mind. Also, if you or your DH had a very distinct and overt reaction to it (good or bad), she could be remembering it more vividly than other things that happen during the day.
That being said, it's good you wen to your Dr and removed your daughter from the school - it'll give you greater peace of mind.