her parents made up the name, but Sildi is a nickname of the Spanish name Casilda
(Casilda>Casildita>Sildita>Sildi). Some authors think that Casilda comes from the Arabic qasida
(a kind of Arabic and Persian poem), but Roberto
Faure suggests a Germanic origin because of the ending -ilda
(from the Germanic -hild
The confusion between S and Z is a usual misspelling in American Spanish, where C/Z/S has the same sound (Sildi, Cildi and Zildy in American Spanish sound the same).
And for the Y as vowel, it is a misspelling in Spanish, but it is not hard to see this use in nicknames (specially feminine) in an attempt to anglicize: Bassy (for Basi, from Basilisa), Emy (Emiia>Emi>Emy)Dely (Adelina>Delina>Deli), Nardy (Leonarda>Leonardita>Nardita>Nardi), Cary