Sounds like a cross between
Derry and
Darryl, neither of which is feminine.
I checked my copy of *Enwau Cymraeg i Blant* and couldn't find any Welsh name like "Deryl" listed in there, either. The closest-sounding, feminine name there was "Derwena" (feminine form of "Derwen" meaning "oak"); and then there was the masculine name of "Deri" meaning "oaks".
I suspect this is an invented name -- unless somebody else here can come up with a history for it.
--
Nanaea