Being the Silver scrub that I am, my ELO tends to bounce between 1200 and 1400.
I do find though, that when I streak myself back down to 1200- I can always carry myself back up with Sona.
At 1200, it seems extremely rare to find ADC's that can actually handle her poke in lane- meaning more than likely, if you play it aggressively, you're going to dominate the lane for your ADC and get him well fed.
I also like to play Sona as a super-fast warding/ward clearing machine who can take a bit of a beating- so my usual build goes like this-
Wards/Pots/Mana Regen opening
Philo Stone + Hon + Boots+5
Chain Vest + Negatron cloak + Oracle to keep myself alive.
Then depending on their team
Chain vest into Frozen heart for AD heavy teams
Negatron into Fon for AP heavy teams (plus the extra MS is fun)
Then the other one from above- but really, the game is usually over around now.
Of course- you won't lose every game since no matter how well you get your carry fed, if your Mid and top lane get themselves dominated, then your ADC will be focused hard - but if you are consistantly winning your lane, then all you need for them to do is break even and you'll win it.
(plus, mid to late game- your superior ward coverage is OP - nothing worse than playing a different role and being left completely blind cause nobody is warding!)