Hey, Rex! Glad to see you. I am super excited myself!

Ah yes! Non humans are somehow much easier for me to describe. With normal people, I guess I just tend to note their clothing and hair in fair detail, eye color and general build but where I struggle is describing their actual facial features, I'm getting better though, at least I think I am.
But yes, I totally understand writing five hundred words of appearance and just being like 'well, that explains a whole lot of nothing...' 

...Yes, right well I understand why you felt a little intimidated trying to describe THAT in writing. It is lovely though.

While the clothing of most of the fairies generally seems to stay quite simple, I see no problem if you wanted to have Iona wearing something more intricate and, given the color scheme, I can totally see the general outfit being made of flower petals.
If you keep the leggings, would you imagine them coming the whole way up to cover her legs? Or the more stocking type things she has on, they do seem to be longer at the back somehow. And yes, if you'd like the lengthen the skirt, I think that'd be a nice idea, it's more of a belt at the moment =P

Maybe, since it has all of those layers bits, the outer layers could be somewhat opaque, that'd be all glittery and silvery and you can go ahead and keep the arm thingies if you like, I like them. The headdress is up to you, seems a bit over the top to me but it is a flower so I think it fits nicely. Maybe minus the darker bit at the top, but if those were representative of storm clouds to you, maybe not.

The arm thingies and the headdress are totally reminding me of when I played the Disney Fairies DS game. There were some intricate and really beautiful designs for clothes in that game, I'm sure they must have had a fashion designer for that game!
 
Anyway, I'm generally liking the reference image coupled with the more modest alterations you're mentioning. When you get it clear in your head what you want, I'd be fine if you just go 'her clothes are like this but...'.

As for her hair, sounds nice, though if you're going to have a headdress like that, you should really have an over the top hairstyle, too =P