Reminding her how beautiful she is comes with making her feel good, and makes you a poster boyfriend. Best of all: simplicity and honesty are all you need. Buy her, say, a card that expresses your appreciation, compliment her at odd times, and if you feel that she's the most gorgeous creature you've ever laid eyes on, be sure to let her know. Women want to look good for their men, and proving to her that you only have eyes for her will be a validation of that.
What it all boils down to is making her feel good about herself and appreciating her in an unselfish way; find success in this department, and she will love you eternally. More importantly, however; if I've just finished describing you and she still takes issue with the little things, then maybe it's time for you to reevaluate how good a partner she really is.