She's only fourteen, it's a school girl crush. Ignoring them won't do much -- either it'll encourage her into trying harder or hurt her. The excitement of an, excuse the phrase, "older man", is probably more appealing to her than anything. At that age girls can be oddly stubborn, even when it's quite clear the person isn't interested. I think, for both of you, the best way would be to explain to her that you're really not interested, apologise, and basically just let her down gently. For all it might be a bit of fun for her, she's still only a kid, so anything too harsh might put her off boys for a while.