I'm really sorry you're going through this. It sounds like schizophrenia to me. My dad's friend had this happen at that age and I know it is actually pretty common for it to come on full force later in life. As for her not believing she's crazy, that is very normal. The best way to help you understand is, What if I told you, you didn't have a mother and father? You'd think I'm crazy. WHat if I got two or three people to tell you the same thing, including a doctor and therapist? You'd think I was trying to trick you and that they were all in on it. What if your mom and dad told you that they weren't your parents too? You'd probably get very upset, why are they all trying to trick me. I know this is real, the proof is right there in front of me. Why can't they see it. I'm not stupid or crazy. (Sound familiar)
The best thing for other's safety sounds like medication, but yes, all of them have side effects, some or more drastic than others but basically all are miserable, there are no ideal options. It's a constant give and take. As for convincing her to take meds, the easiest way to gain compliance is have her decide what would make her enjoy life more. Lead her to wanting something to help make her not so sad or anxious. But telling her it will 'fix' her 'symptoms' will likely make her push against them, or lie about taking them. Remember, in her mind, she is not the crazy one, you and everyone else who tries to tell her otherwise are the ones trying to trick her and are conspiring against her, and at some point she may even think the enemy has not only gotten to you (as in hurt you) they have also managed to trick you into becoming one of 'them'. I hope she is able to get some help.