These are two of the best YA fantasies you've probably never heard of. It's not surprising that Youmans's novels aren't well known. Although the writing is appropriate for young adults, the main character in both books is a young girl (too young to have a boyfriend, though there are hints of future romance in both stories), which probably makes them less appealing to teens and adults and more appealing to MG readers. Unfortunately, despite beautiful and terrible magical creatures rooted in American folklore, heroic but deeply personal quests, and rich, descriptive prose, the pre-modern setting, the complete lack of traditional monsters (no werewolves, vampires, or zombies) and an absence of hawt teens lusting after each other makes these books a pair of sadly overlooked gems that will never get any love from Hollywood.
The setting for both novels is Adantis, a magical land deep in the Appalachian mountains inhabited by a mix of the early border-Celtic settlers from Ireland, Scotland, and northern England, and the Cherokee who escaped the Trail of Tears. It's not just the people who are an intermingling of Old and New World blood, though -- there is magic, and magical beings, from both worlds as well. Youmans grew up in this region and draws on traditional legends to create an original fantasy world based on the old stories but with original embellishments of her own.
The Curse of the Raven Mocker and Ingledove are stand-alone novels. They both take place in Adantis, but all the characters are different. Youmans used similar plots in each of them: a young girl discovers that her mother was originally from Adantis, and she must go there to save someone. In The Curse of the Raven Mocker, Adanta follows the Raven Mocker (an evil Cherokee sorcerer) who has abducted her mother; in Ingledove, Ingledove and her older brother Lang go to Adantis to see the land their mother came from, but then Lang falls prey to the seductions of a lamia (an evil creature known to both Old World and Native American mythology), and Ingledove must save him. Adanta and Ingledove are both brave young girls, but they're completely realistic: when confronted by dangerous magical beings, they're quite naturally scared out of their minds, but force themselves to press ahead anyway.
These are very literary novels, despite being aimed at a younger audience. Youmans doesn't skimp on description and metaphorical flourishes, and she conveys a lot of depth in a few sentences. The prose is lush, meticulously detailed, and full of uniquely American bits of flora and fauna and folklore and culture. There's a lot of thematic depth to them as well, though most of it won't go over the heads of younger readers. Both books have bittersweet endings.
I'd highly recommend these books for any preteen or tween, but as someone well beyond the "Young Adult" category myself, I can say there's much to savor even for older readers.