It's pretty, but it is a bit odd. I don't mean that in a disparaging way. You have to embrace its different-ness rather than worrying about it. It won't be any more difficult for a child to spell than any other name.
Lily Eilonwy is really pretty - it's hard to make a nice combo where both names end in that long ee sound, but this one works.
Lillian "
Lily" Eilonwy would be pretty too.
Have you thought about how you'd combo it as a first name?