Eulalia

Olalla and Lalla are Spanish diminutives of Eulalia.
According to some sources Eulalia, so popular in Spain, was introduced into England during the Middle Ages, and was mispronounced as Hilaria. Such sources see Hilaria during the Middle Ages as a form of Eulalia rather than a feminine form of Hilary.

The name derives from "Evlalos", an epithet of god Apollon in Greek religion. The feminine form "Evlalia" (Eulalia) was a very common Greek name in Ancient Minor Asia.