They suggest you order a size smaller than your regular size so maybe if you order the 9 toddler instead of the 8 that will give her the room you are looking for. You could also call ugg and ask them....you don't want them too. If or the will not wear well...
Size 6 M US Big Kids will be the correct one.
UGG generally runs big, but I would get the 11 so the kid can also grow into it and wear it more than just one season.
No. I bought water protection for my uggs to save the color as the water will change it and to keep the water out.