Fast hooks are Sona's worst nightmare. Thresh is the only hook I'm not afraid to death of.
As far as builds go, ap seems to be the thing people are going for. Everything she does scales with ap anyway. More ap = more team support, unlike other supports that really just throw out stuns and item actives. To boot, she can double as a secondary source of ap damage.
I don't exactly care for Frost Queen's Edge since it's built into her q. Just sit on the tier one and build everything else, imo. I personally go
->
->
->
->
. By then the game's usually winding down, but for a 6th item, I was probably gonna toss in
. Too bad I can never afford it. =/
Edit: I know people suggest things like Frozen Heart, but I'd only suggest going HAMM on defensive items if you're dying too much. I average 4 deaths a game for 16 assists, so I've come to the conclusion that I'd benefit more from something on offense than on defense.