The 15-year-old victim was assaulted in Kettering town centre on Tuesday, July 25.
The teenager was with a group of friends who were near the water fountains in Market Place, between 7pm and 7.30pm.
An argument between the teenagers and an older woman also in Market Place took place which resulted in the woman punching the 15-year-old in the face, grabbing at her neck and attempting to bite her.
The offender was white, about 40, of large build and with blonde hair, with black extensions.
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She wore a black top with a flower on and black leggings.
Officers would like to speak to anyone who may have witnessed this incident or who may have any information regarding it.
Witnesses or anyone with information about this incident can contact police on 101 or Crimestoppers anonymously on 0800 555111.