How can I convince my paranoid friend to get mental health help?

DEAR ABBY: How do I tell my friend I feel she needs a mental health evaluation?

She has been my closest friend for 20 years, and we have been through many trials together. She has been married for a couple of years to a man who seems very nice. 

Abby, she is convinced that she’s being followed, but doesn’t know by whom or why. She tells me about terrible arguments she has with her husband because she thinks he orchestrated situations in public places.