If this was reversed and it was an 18yo boy looking at a 14yo girl, we'd be horrified. Things don't change just because the younger party is male. He's still a minor, still a child.
The 18yo can think what she likes, but should keep those thoughts to herself. Kissing might not be illegal, but it feels all kinds of wrong to me. I'd be asking myself why the 18yo can't find someone her own age, why she needs to be putting the moves on a child.
PPs mentioning later in life age gaps have a point, I will concede - if he were 27 to her 31 we wouldn't be having this conversation, but he's not 27 to her 31, he's 14 to her 18, he's a child (I can't emphasize that part enough) and all of this justification and "rules lawyering" to make it sound like it's okay that a woman of the age of majority crushing on - and potentially acting on said crush with - a child under the age of consent is just revolting and frankly frightening.
If she likes him that much she can wait until he's old enough - legally and emotionally - to give consent. Until then, it doesn't matter what she thinks, she should damn well look somewhere else.