I would pronounce it "line" but I know someone of that name that pronounces it that way. A beautiful name that was on our short list. Ended up going with Emilia though, and I am sure that she will be spelling her name her whole life as everyone thinks it is Amelia.
I am sure that I watched a movie with a girl called emmaline pronounced "line" in it recemtly, but i can't think which movie it was!