Cherin was the name of a legendary king of the Britons in Geoffrey of Monmouth's Historia Regum Britanniae, likely related to IrishCiaran, but this seems an unlikely source for Cherin as a feminine name.
Cite as: J. Uckelman, S.L. Uckelman. "Cherin". In S.L. Uckelman, ed. The Dictionary of Medieval Names from European Sources, Edition 2023, no. 1. http://dmnes.org/2023/1/name/Cherin.