Heliabel

The Damsel of the Sanct Grael by Dante Gabriel Rosetti

Heliabel is a name taken from King Arthur chivalric romances outside of the Vulgate cycle. In The Evolution of Arthurian Romances by James Douglas Bruce, he claims Heliabel, alternatively spelled Helizabel, was a corruption of Elizabeth. If this is the case, it might not be wrong to assume the pronunciation is hel-LY-za-bell. That does not mean Heliabel is pronounced hel-LY-uh-bel, because pronouncing it hel-LEE-uh-bell seems more intuitive, and there are rumors that this spelling was influenced by Greek helios, meaning "sun." Bruce says these are "obviously mere corruptions" of Elizabeth because in other versions the character King Pelles's daughter is named Elizabeth after John the Baptist's mother. Elisabel was found as a variant of Elizabeth in medieval French. In a review written for an article by Ferdinand Lot, found in Romantic Review, Volume 10, it says that Heliabel lost her virginity to Lancelot, and that sin caused her to change her name from that of John the Baptist's mother to a secular one, Amite, and that this specific storyline is only found in the Galahad Queste.

Heliabel is a princess, the sister of Perceval and found specifically in the Grail romances, and she is likely the same character as Dindraine, or even Elaine (I haven't read all of these stories but it seems in some that both Elaine and Heliabel/Helizabel are considered the mother of Galahad, depending on the author, and that her named was changed to Elaine post-Vulgate, and it may have seen the spelling Helaine first). It is not uncommon for character names to vary in spelling from author to author in these romance cycles, even to the point of seeming like a completely different name. Also depending on the specific work, Heliabel is sometimes left behind shortly into the story, and sometimes she plays a much larger role. For the most part, her destiny is to be the "Grail Bearer" by giving birth to Galahad, christened after his father Lancelot's baptismal name.

This name is so rare that it has no U.S. data. Regardless, the fact that it has been used in literature and the possibility of honoring an Elizabeth in your family (with a fun story of the literary Heliabel honoring an Elizabeth), or the potential use of nicknames like Hellie, Hebe, Lia, or Belle, make this a solid choice.