It is claimed she was trapped in a shower block near the camp but loud music meant her cries for help went unheard during the horror attack.
The woman was told not to report the alleged crime by colleagues working for far-left group No Borders, according to reports.
They are said to have told her speaking out would have damaged their cause – to support freedom of movement and oppose migration controls.
She reportedly remained silent for over a month as a result.
She and her colleagues were stationed at a makeshift camp in Ventimiglia, Italy, on the border with France.
It became a flashpoint at the start of Europe's humanitarian crisis earlier this year after a local crackdown on border controls.
Last week police cleared the camp – which housed around 30 migrants and 20 activists – with tents and personal belongings removed by lorries.
They refused to budge for most of the day – and only agreeing to move after the BISHOPof Ventimiglia intervened.
The town's mayor said: "This situation could not go on. We understand why they are protesting but the camp was illegal."
The woman has not been identified but is thought to be in her 30s, according to Breitbart London.