Assalaamu alaykum. A group of protesters all of the sudden showed up. There was a female Muslim who was nearby, and one of the protesters captured her in their video without her consent. She was unable to verbally ask that person to blur her in their video, but she attempted to use her hand to tell that person that she does not want to be in the video, but it did not seem to her that the person understood her since they were chanting and nodding their head. The female Muslim wanted to go up to them but was uncertain whether that protester would be violent or not, and even if she went up to them, the other protesters might capture her in their video, or the person who was recording her could have been broadcasting live, and there is nothing that person could have done for her then. So the question is: is this female Muslim sinful? Please understand that this was the first time for the female Muslim to see protesters in front of her in real life.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger. 

If the situation is as you mentioned in the question, then this woman has no responsibility for what happened in being filmed, and she is not sinful, as she did not choose to do so and had no control over it.

Allah says (what means): {And there is no blame upon you for that in which you have erred but [only for] what your hearts intended. And ever is Allah Forgiving and Merciful.} [Quran 33:5]

Allah also says about the supplication of the believers (what means): {Our Lord, do not impose blame upon us if we have forgotten or erred.} [Quran 2:286]

It is proven in Saheeh Muslim that the Prophet said that Allah said after this supplication of the believers, "I have indeed done so”; meaning that they are not held accountable for this [forgetting or erring].

Allah knows best.