So I am in the process of making a companion mod, this will be my first real/companion mod ever. So I currently have parts of the dialogue set up, mostly just that of first meeting this person. I have it set that if you walk within 50 units of the person, she will walk up to you asking for help for instance. As soon as that dialogue box starts up, I want the marked quest to activate.

What exactly do I have to do to achieve this?