They met years before, when the girl was still a child.

The elf had business around the border, likely along the lines of killing some wild creature out of control, something big, dangerous and magical...And whether he came accompanied or not, he goes back alone after as he realizes he lost something. Jewelry or a trinket of sorts, something very important to him (possibly something meant for a future wife, because of course I went there).

 

What he finds instead is a little human girl, traveling with her teacher...at least until she wandered too far and got hopelessly lost. It's getting dark and starting to rain, so she's pretty fortunate that, despite the history between their kind, he offers to help.

 

They find shelter and he promises to tell her the way back in the morning. In the meantime, they talk. Eventually, just as she told him how she got lost, he admits why he's there.

The girl is rather floored such a nice person lost something dear to them, and that now it'll probably get washed away by the rain or buried in mud. As he was so helpful, she decides to use her own powers to make something and offers it to him to make him feel better. Likely nothing as impressive as intricate elven craft, but maybe it could be his replacement....lucky charm or whatever. He wasn't clear why it was important.

Though clearly she has no idea as to the significance of what he lost, it's a nice gesture, and he sees no harm in accepting.

 

Come dawn he keeps his word and walks with her a ways, then gives her careful direction, and she makes her way back easily.

Later, when out with her tutor, now under more careful supervision, she finds something resembling what the elf described. Alas, though she wanted to return it, he had since left.

She'd just keep it. People didn't get around elves much, but her Teacher sure did a whole lot more than most. Maybe she'd be able to return it eventually.