How important is a smile?

My friend Tracy came up to me a few days ago when i was with my other friend Kelly i don't think she likes her to well cause she likes to tease her a lot, so she starts talking about how smiling is one of the most important things to getting a serious relationship and that every guy looks at a beautiful smile but my friend Kelly has a detchure in her front tooth because when she was younger a boy knocked it out, she thinks she has a really ugly smile and that no one will ever marry her, she can't seem to get a boyfriend, she's so insecure about it i feel horrible when some of my other friends compliment on my smile, because she'll just put her head down and you can tell she's trying to hold in her tears, i really want to cheer her up, i try to tell her she has one of the most beautiful smiles because she does but she always says im just trying to make her feel better, can anyone give me an idea to try and help my friend?