your situation is actually complicated. first of all, to gain trust, one needs to see you personally i think. you have to look her in her eyes and say whatever you feel for her. but if its not possible to meet up, then you just have to call her. you can tell from someone's voice if he is sincere or not. just be honest, dont focus too much on what will she like to hear as this might veer you off to the wrong direction. let her know why you like her, and tell her that you've been through the same thing ( depression ).