I feel like the EHM-ə-leen pronunciation sounds too close to the EHM-ə-lee pronunciation of Emily, which is why I prefer to pronounce it as EHM-ə-lien.
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.