Ok, this might be going to be a bit dry, but have you ever thought about why Lili pronounced “Flynn” as “Fleen”? As 1/4 of a linguist, I became interested in this question, and here's what I found out.
Even though I never heard Lili speak, I believe she did not say “Fleen” directly. You probably know that in your English language, you have got two i-sounds: a short one as used for “Flynn”, written something like this in phonetics: [ı], and a long one, like in “seen”, represented as [i:].
Now in the French language, there is nothing like this – the poor French have only one single i-sound, represented as [i]. Its length is something in the middle of the two English sounds, but supposedly, for English-American ears, it sounds like a long [i:]. That's why Errol probably chose the spelling of “Fleen” to represent Lili's accent.