She is really strong with short trades, but if you all in a Sona lane she just dies so quickly. She's also really vulnerable to ganks because she's immobile and squishy and bot lane is a really long lane. You really need your support to trade with you against her, or you need them to be able to all in her. If your support offers no pressure in lane it's just lost.
She has really good strengths and some awful weaknesses. She can really hit newer players hard as she's not often picked and playing against a champion that is a natural trader will always be hard in lower elos because sona players have to express less skill than you to win trades.
By natural trader I mean, has a point and click trading ability and a defensive tool that allows them to win short trades for free. Panth with Q and his passive, Nami W and Sona with Q Chord and W. There are probably some others but those are the ones I have off the top of my head.