biting 5 year old

[cascade]

My dd today decided to bite her best friend on the face. I am completely horrified. She has never done this before and she wouldnt give a reasonable explanation as to why she did this. Is this normal, im actually really worried as her behaviour at school has been great, but this week from what i gather from the teacher it has not been good. Nothing at home or school has changed. Why would she attack another girl so violently. I would expect this from a toddler but not a 5 year old. Im not sure how i should deal this with her as it is so out of character.

my son went through a phase of doing this. it was put down to frustration, just acting on their first reaction. i had to do a star chart (which worked) for daily good behaviour, but he did it on and off for a while. awful isn't it

i was holding my head in shame as the teacher spoke to me.

i know it makes you feel so useless doesn't it.

it was probably just a one off incident, maybe she's had a row with her and doesn't want to tell you?