This is inexplicably my newest and biggest crush. Setting aside the association with the somewhat unbalanced lover of Oberyn [name_m]Martell[/name_m] and mother of the Sand Snakes, I actually really, really love the way it looks and sounds. I think it fits in pretty well with current giants like [name_f]Emma[/name_f], [name_f]Ella[/name_f], [name_u]Arya[/name_u], etc. Although I prefer [name_f]Ria[/name_f] as a potential nickname.
Thoughts? No idea what would work as a middle.
It looks pretty in writing but how do you say it?
[name_f]Ell[/name_f]-ARE-ee-uh. Think Elle and then add Arya.
I agree that it looks very pretty written down, but it does look a little made up. Like you said though, I dont see why it wouldn’t work as its similar to [name_f]Emma[/name_f], [name_f]Ella[/name_f], etc.
It is made up; it’s from the mind of [name_m]George[/name_m] R. R. [name_m]Martin[/name_m]. But people make up names all the time. They add “leigh” or “lynn” to names that didn’t include them originally, or combine two names, or use a season or fruit or animal that was never previously used as a given name. To me this is much more elegant than many of the “kreeatiff” names we have floating around now. 
GRRM has such gorgeous names in his book. I definitely like Ellaria or even Elaria as the spelling. There is also Ilaria which is a name with history prior to ASOIAF (it’s an Italian name I believe) and I think it’s pronounced the same or very similar.
If you’re comfortable using a name that doesn’t have history outside of a certain fandom/franchise I say go for it. It’s a beautiful name and you wouldn’t be the first person to do so (Wendy anyone?). It won’t be everyone’s cup of tea because a lot of people shy away from “made up” names (understandably so, some are just ridiculous although some are gorgeous and some “Real” names are ridiculous). Just do what feels right for you
[name_u]Haven[/name_u]'t seen the show so haven’t heard the correct pronunciation so I read it as [name_f]El[/name_f]-ah-re-uh. Like [name_f]Ella[/name_f] + ria. Seems like it would work just fine although I’m not sure I’d want to be related to anything to do with Sand Snakes, although maybe that is actually a good thing.
It seems to me that either a very short or very long name would work best in the middle w/Ellaria. I don’t know what your style is, but if I were to use Ellaria, I’d think about:
Ellaria [name_u]Wren[/name_u]
Ellaria [name_f]Rose[/name_f]
Ellaria [name_f]Fern[/name_f]
Ellaria [name_u]Ren[/name_u]ée
Ellaria [name_f]Anneliese[/name_f]
Ellaria [name_f]Alexandrine[/name_f]
I pronounced Ellaria el-AHR-ree-uh when I saw it written down, so you might get that pronunciation quite a bit. I’m personally not a great fan of recently coined names though, so it’s just not my style. Nice sound. As @trippindippy suggested, [name_f]Ilaria[/name_f] is a beautiful option that has history as a given name (Italian form of [name_u]Hilary[/name_u], so it has a lovely meaning too)
I don’t know what it is, but I still love Ellaria more, even though it’s nice to know that the [name_f]Ilaria[/name_f] options exists. 
I figure she could always use [name_f]Elle[/name_f], [name_f]Ella[/name_f], or [name_f]Ria[/name_f] as a short form if she really wanted to find her name in a baby book or on a key chain or something. [name_f]Ria[/name_f] remains my preference. I had a friend named Dawnielle in elementary school, and she’d go by [name_f]Dawn[/name_f] sometimes when she wanted a name that “fit in” a little more. Now she mostly goes by the full Dawnielle, though, and it fits her really well. She remains the only one I know, although there are a ton of Danielles my age floating around.
Re: the Sand Snakes. Ellaria Sand is a tad nuts in the books and show, but she’s still a pretty tough character. And her daughters (the Snakes) are definitely not women you mess with. I consider that a good thing. 
Anyway. Many thanks to everyone for their replies and suggestions. This is a really recent obsession, as I mentioned, and I just can’t seem to kick it out of my head.