I have loved this name since the early 80s from the film The [name]Blue[/name] Lagoon. Also, the lady in the 1963 film It’s A Mad, Mad, Mad, Mad, World was named [name]Emmeline[/name] too. Anyway, I had a baby daughter in [name]April[/name], and we named her [name]Katherine[/name] [name]Noelle[/name]. I really loved [name]Emmeline[/name], but my sister has a daughter named [name]Emily[/name] [name]Rose[/name]. Therefore, I thought it was too close to her name. The only drawback with this name is that so many people mispronounce it as [name]Emma[/name]-leen or [name]Emma[/name]-lynn. The second syllable is a long I like in [name]LINE[/name]. The French version would be Leen. Any opinions? Or would there really be no problem with this beautiful name.
I love [name]Emmeline[/name] but if I were in the same situation with a niece named [name]Emily[/name] I’d have to let [name]Emmeline[/name] go. 
I have a niece named [name]Ava[/name] and I wont touch [name]Avery[/name], [name]Eve[/name], [name]Eva[/name] or even [name]Ada[/name]/[name]Aida[/name] (which I love) because I think they are all to close to [name]Ava[/name].
I’d say unless you see your niece fairly often, you will be seeing your daughter much more often and presumably it wouldn’t be too hard to differentiate the names if you were calling out for your daughter while your niece was around. This reminds me of a few friends of mine - [name]Stephanie[/name] and [name]Jeffrey[/name] who were brother and sister but when they were called [name]Steph[/name] and [name]Jeff[/name] they were constantly confusing eachothers names for the others. So - I guess what I am getting to is that if you really love the name, you should go for it and I am sure each will have their own nn’s that will be different enough to differentiate them.