Lilou is very old name in salalah city. My mother name Lilou she is 80 years old. There are around 40 females in the world use this name (before the 5th element film) all of them over 40 years old. This name only in my city no other arab country or even in my country use this name. This name 100s years old. No meaning of this name I think it is from lila as easy way to spell it.
It CAN be a nickname but it's not where it comes from as a stand alone name at all.It first appeared in 1997 and comes directly from the movie "The Fifth Element" which was released that year. In this movie the main female character is named Leeloo, which was written phonetically by parents 'Lilou' (the name is not written in the movie).The movie was a great success in France, hence the apparition of the name. Then it went viral because Lilou goes perfectly in the trend of cutesy L names given to girls these days.
In France the name comes from names that end in the sound -li or -lee, with the addition of -lou as a sign of affection. My daughter is named Olivia Louise but goes by Lilou in school and at home.