Hi. I have a friend who has had a crush on a classmate in high school, for 4 or 5 consecutive years. She buys his laundry detergent, so she can smell like him, and although she likes him, which is an understatement, she will not talk to him.
She has been creeping on him for so long, and will not let it be. How do I convince her that she has a problem and needs to seek mental help?
LemonVibe 
You do not. Keep trying to though. I feel like eventually she’ll get rid of you and be free of people who aren’t licensed professionals who judge her as mentally ill when she’s just got a normal crush.
Just leave it alone and change the subject. Do not gaslight her that she’s crazy. You are not a psychologist and she’s hurting no one. What will be hurting her is to say something that hurtful. If you are really tired of the subject tell her you don’t want to hear about him since the situation never changes. Since you are so focused on what is essentially someone else’s romantic beeswax, I think it’s time to focus on your own issues and get busy doing something else, like a job, after school actives, volunteering or sport.