I don't think I'd assume
Edie was a nickname for
Edith, especially where I live (England) nickname names aren't exactly rare. But I wouldn't be surprised if it was short for
Edith.
I really like
Edie as a first, or a nickname for
Edith. But personally I prefer using given names more than nicknames, so I'd use
Edie in full if I liked it enough to use. I have both
Edie and
Edith on my list.
I don't see
Edie as trendy in the way
Avery, Everly,
Payton etc. are. Again, from a U.K. perspective it fits the trend of nickname names and vintage style names, plus it is increasing in popularity so it can be described as trendy. But it's not a more modern, unisex style trendy name like the ones mentioned.
Fangirl (18) Dreaming of...
✦ Pandora ✦ Evanthe ✦ Marigold ✦ Beatrix ✦ Demelza ✦ Fae ✦ Sally ✦ Lavender ✦ Sybil ✦ Anna ✦
✧ Caspian ✧ Phoenix ✧ Ptolemy ✧ Horatio ✧ Nikolai ✧ Artemus ✧ Indigo ✧ August ✧ Lorenzo ✧ Prosper ✧
http://www.behindthename.com/pnl/1396