If you're going to pronounce it mar-leen, then spell it that way to avoid confusion. But I don't like it with two syllables at all unless it's a mn for
Lili! And even then, half the time in the song it's Mar-le-ne, isn't it? Wie einst
Lili Marlene (3), wie einst
Lili Marlen' (2)
This makes me sound like the cultural snob I no doubt am, but
Marleen suggests a namer who doesn't know
German at all, can't be bothered to find out, knows that most of the time in English the -e at the ends of words is silent, and goes happily down-market while chewing gum with her mouth half open.