hm, usually the name of a pony has something to do with their special talent. names don't have to be as obvious as Cutiemarks but if you look, you will notice a link.
if i look at the name River Dream, one of the first things that comes to mind is something that has to do with water. maybe she could have a talent for sailing on rivers?
for the dream part, maybe her colour scheme can have these dream-like colours. pony names occasianly have something to do with a ponies look aswell, like Pinkie Pie who's pink, Rainbow Dash who has rainbow hair and possibly Twilight Sparkle who has dark, twilight-like colours.
these are just suggestions