What are the observer's options if she doesn't have a witness for the trespassing and assault charge?

Observer witnesses wild horses illegally rounded up on free range land and herded into pen on private land. The observer sets horses free but is assaulted when she tries to leave. She defends herself with a knife and inflicts minor injuries on one of the assailants. She is badly beaten. She is detained and taken to emergency room and charged with trespassing and aggravated assault. There are only 2 witnesses to the actual assault and altercation. Observer has no witnesses.