Well, the normal way this spelling would be pronounced according to English orthography is with a short "i", like LIL-uh. When doubled consonants follow a vowel, the preceding vowel is almost always short. You can see this in the word pairs biter/bitter, later/latter, pined/pinned, filer/filler, tiled/tilled, etc.
Lilla might be pronounced LEE-la in some other languages besides English. But I think it is unlikely that the spelling Lilla is pronounced as LIE-luh in any language I know of.