Lenne's name is obviously of Western influence. Sometimes girls have the nickname "Len", but it doesn't have an origin. There are, however, some other names similar to her's.
Lena means "Illustrious" in Hebrew. There's also Lenore, which is greek for "Light".
Lenne's name in written Katakana is レン, Pronounced as "Ren". The L's are replaced by R's in Japanese. However, their R is not like the German R, or the retroflex American R. R's in Japanese sound very much like an L.