Well Photoshop can still make miracles.. It was able to trasform it into a 1920x1080 image with a very very little loss of details.. It's not in HD but it doesn't get ruined if put as a wallpaper.. But I stayed to 1360*768 resolution, my monitor is full HD but my ati radeon 9200 doesn't work properly with that resolution.. And also my notebook has a resolution like that..
Anyway, talking about the picture, you did a very nice job, and the lighting is just.. wow.. and of course, she's Rainbow Dash lol, so it's even 20% cooler xD