I'm not experienced with fantasy looks, and hopefully others here with that expertise will give you some ideas, but since no one has answered yet, I'll give some initial thoughts --
Image is a bit small for my myopic eyes,

but it's a cute idea with two adorable looking girls. To my eye, however, the highlights and some of the midtones are too bright and have lost detail, and the girl on the left has a blurred dress which disappears into the blurred petal. I would look for another background flower because this one has a petal (or other flower part) at a diagonal to the second girl which will probably distract from the girls -- but I don't think that blurring that element is helping the overall look. I'd find another background -- one that didn't have any distracting elements near the girls.
I'd try to retain all the detail that I could and then play with the overall image to give it a fantasy look -- by adding a soft vignette around the image or adding a duped layer that has been blurred a bit (playing with layer blending modes to see which would give me a look that I liked) or adding fairy dust, etc.
I like the concept, and the high-key look will probably be effective also. The girls are lovely and could easily be fairies. I hope some others here will give you some useful ideas. Keep working on your concept -- you'll get it the way you envision it if you keep your goal in mind.