You're in a legal position to get some sort of injunctive relief against your mother. Bi-Polar is recognized medically as a form of schizophrenia. She's "disabled" in a sense where she's capable of creating legal problems for you because of her psychiatric instability.
Since you can't afford an attorney -- (It might cost you $500, and the State Bar might be able to provide some aid "pro bono" because it needs to be taken care of.) Since you can't afford an attorney, you should contact County Social Services, Dept. of Human Resources about having your mother assessed, diagnosed, and otherwise restrained from making unfounded charges against you.
A social worker can help present your case to the police. Sounds like no charges are being filed. You should be able to have your guns returned to you without any sort of complications.
The "issue" is the mental state of your mom. That needs to be addressed, and social worker should be able to help you with that.
Good luck, and keep us updated.