Eryn is similar to regular Eagle Girls with slightly better Magic, and despite her proclamations doesn't make that good of a hatcher herself, even fully leveled. It is recommended to get her Incubator trait on a more Magic focused unit. Interestingly, Eryn's sex skills are pretty high so she is a decent Brothel candidate.
Her other trait, Mending, is also quite rare, so recruiting Eryn is an easy way to obtain it.
That said, do note that Eryn is large sized and a Mercenary, so the daily drain on your resources is higher than most other units. If you're not interested in obtaining her traits, she may not be worth your time.
Can't be changed with gender potions.