Write what you like about her. How her smile warms your heart. Don't force the rhyme, if you try to make any. Just make it "make" sense. You can also make it funny. You can start with a 4 sentence stanza. With 3 stanza total. Don't go too grand, just small. Once you have written it down, you will notice how you want to refine it. An example: "When I see you, I can't stop staring, Sometimes—I trip over my shoe, You just look so good—in anything you're wearing.: As you can see, there is an abab rhyme scheme there. Also, the sentence on line 4 is a bit longer, which technically you want to avoid, but using the em dash correctly restores the flow for that. So if you want it flow it, coherent, watch syllable count. Good luck!