Respect her. Love her for who she is and let her know that. Next time she has a problem, just say "Babe, I know you upset, but I just wanted to let you know that I love you and nothing is going to change". That'll work wonders. But, the key thing is, don't just tell her how much she means to you, SHOW HER. Ever heard of the phrase "actions speak louder than words?". If she's not feeling well, bring her over some soup (corny, but it'll score points), if she is stressed out, take her on a surprise picnic by a lake or at a park, if she just needs you to be there for her, then do it. That's why I am still with my girlfriend (a year and 5 months), because I don't just tell her how much I love her, I show her. If your girlfriend really means that much to you, finding ways to tell her and show her should come almost naturally. Good luck.