Found: YA Fantasy, young girl protagonist who needs to learn magic

I'm pretty sure I read this book about 5 or 6 years ago. I can't remember a lot of it, but the protagonist is a young girl and I'm pretty sure she has a younger brother. Don't remember any names. She starts off in her village and she and her brother collected syrup from the trees.. but they stay out too late and end up getting stuck in the dark(?) world. I don't remember if they're called "dark elves" or "nightlings" or something but the king is trying to get her to marry him I think. So she has to learn magic to prevent all that or she'll be stuck there forever.

I do know it was part of a series, I'm not sure if it was a trilogy or not but there was definitely a second book that I never read. I would to hear if anyone knows the name of the series or has read something similar. Thank you!

>1Sounds like it could be THE RUBY KEY by Holly Lisle, part of her Moon and Sun series.
(Off topic: You'd probably enjoy The Hollow Kingdom series by Clare B Dunkle)

>2 Jen-the-Librarian: Yes! That's it! Thank you so much!

Touchstone: The Ruby Key by Holly Lisle