She's more likely to listen to a therapist than you

I am embarrassed in a way to even write this question. My daughter is way too serious with her boyfriend. They are both in high school and they are both 17. She is going to college next year and he is not. They are both so young. Now they are fighting so much about what they will do next year and she is very depressed and worried that they will drift apart once she goes away to school. She wants them to go to couples therapy to strengthen the relationship. She has even talked about marrying him before she goes!!! I find the idea insane but she is so distraught and she has been almost hysterically worried and upset for more than a month. To the point where she is losing weight because she can’t eat. I am not sure what to do with her. Should I support this idea? The last thing I want is to see her run off and get married. Would a therapist help them to realize how they need to keep their options open? They do not listen to me anymore. They are just children still. He is a nice enough boy but the whole world awaits her and she needs to see this. I was trying to just let things run their course but I am worried they are going to do something rash.