I don't really think it's a stretch. I mean
Cate is usually pronounced like
Kate (actually it's always pronounced like
Kate) and -line is commonly pronounced as -linn, -leen, and -line. So I think it's possible to use that pronunciation.
But I agree that KAT-e-leen is probably what most people expect and I really like it so it's probably what I'll go with :) Thanks!
I know it's only for a character but I need to pronounce it in my head, even for writing a story. Plus what if they'll make a movie out of it? :P