Not that I played competitively at the time of SC3, but I've seen a number of things that sophie has there that are noteworthy:
66A+B 66B juggle ender gives her a ton of damage off of many standard launchers
A+B aGI returns very high damage when successful (80+ for a vert and 100+ for a hori)
AS B does more damage as do the 4s (I think AS B:4 is 70 in SC3)
an arsenal of pokes with impressive frames and/or properties; 3K, AA, WR B, WR K to name a few
her 2BB string is easy to CH confirm, with respectable damage and 2B is a very solid poke by itself
236236236236236... reliably ducks/evades a large quantity of moves
As Idle mentioned, her unblockables are sped up considerably, making them difficult to deal with