We named our daughter Emmalene because we loved Emmaline, but not with the "line" pronunciation. We didn't want to have to constantly explain to people that it was pronounced Emma-"leen", nor did we want our daughter to have to explain this. Rarely people have trouble with Emmalene and say Emma-"leany".
There isn't just one right pronunciation of this name. Ever since it was used it has always been pronounced as either Emma-line, Emma-leen and Emma-lynn so you can just choose the pronunciation you prefer. I like Emma-line.
I really like this name - Emmeline and Emmaline. I think that, truly, the name can be pronounced Emma-LEEN, Emma-LINE, and Emma-LYNN, and be accepted. There's not one specific way. Remember Emmeline Pankhurst? Her name was pronounced Emma-LINE.