How do I help my mother and cope with her mental illness?

My mother was diagnosed with Paranoid Personality Disorder last year. She is 45 years old and her condition seems to be getting worse. She refuses to believe that anything is wrong with her, which also means that she refuse to go to a doctor or take any medication. We have tried to put the medication prescribed by the psychiatrist in her juice, but after getting caught by her once we stopped doing so. Me, my father and my brother are the only people she trusts and we can't risk breaking it. She is also getting a depressed and tried told my father that she's leaving home, a few days back. I am an 18 year old girl and am with my mom all the time as she believes that my friends are evil as well and doesn't allow me to see them. Please tell me how a can help my mother and how I can cope up with her mental illness as well as the social isolation she's put me in. I have always been quite mature for my age, and mostly have been able to handle this situation on my own, but I don't know how much longer I can take this stress. I would feel better if I were allowed to see my best friends but that's not possible right now. I know that I can refuse to listen to mom and go ahead and meet my friends anyway (I mean, it's not like she can physically stop me), but I don't want to do that because it will hurt her and make her really upset. And according to the psyciatrist my dad is seeing so he could help my mom, if we criticize her or behave rudely with her, it'll push her over the edge. Oh and I won't be leaving for collage as it's near my house and my mom wants me to stay with her. Any help will be appreciated. Thanks.