How do you tell a loved one they need help?

Hi Reddit, I'm hoping you can help me! I believe my sister in law is schizophrenic. She believes her neighbours are watching her, trying to poison her dogs, spying on her, etc. She also has started accusing family members of conspiracies that range from causing brain cancer, to rape, to drugging her for her entire life, to burying bodies in her childhood back yard. She needs help, and her immediate family doesn't seem to see a problem. They're response is "she's just quirky". She's also started talking about how her life isn't worth living. How do I approach her and let her know that I love her, but she needs a psychiatrist? I'm afraid that if I bring it up she will just lump me in with everyone else she feels is conspiring against her (I should note, she already thinks I don't like her for whatever reason - I'm not sure as it's not true). I'm hoping that you all can provide me some insight into how to be compassionate and understanding, but also helpful? I'm worried she might hurt herself.

Thanks in advance, and yes this is a throwaway account (for her privacy).