Not even on a gameplay level, but the psychological aspect of getting into a fight and then pulling back for a more opportune moment and then watching as all of the enemies health gets restored in about a minute is just demoralizing. Every time the loading screen comes up and I see Sona on the other team I just want to afk right then and say f**k it.
There is no effective counter. She's a stupidly designed champion that excels at both defense and offense, and it's not uncommon to see Sona as #1 damage with like 200k healing done since her "rework". Unfortunately, master level Sona gameplay is still pretty much smash all buttons every time they're up. Fucking terrible.
And if you can't do any of these, then it's probably gg. Sona doesn't have 70% win rate for no reason.
Just focus on strategically holding ground. It's not who has the most kills, it's when they happen. If you need to self ace to get everyone healed so you can push back, that might be your only option.
The same way you deal with any team with a sustain advantage: focus on pushing. It's pointless to focus abilities on harassing the enemy team when Sona (or any healer) can just negate any damage you manage to land. Instead, concentrate on clearing the minion wave. (Easier said that done sometimes, depending on team composition.) But that's what you do -- do your best to shove the enemy team to their turret and siege away.
If your team has poor wave-clear -- or the enemy team has superior wave-clear -- ask, cajole, beg, or demand that your melee champions buy a Targon's Brace (or a Runic Shield, at the very least). That item alone puts melee-heavy teams on equal footing with AOE/pusher ranged champions. Recognizing how amazing Targon's Brace is for melee champions is something that differentiates the ARAM Bronze tier from the ARAM Gold+ tiers.
You need some serious engage and an organized team to take her out and make her lose the game. Otherwise it's a painful and very frustrating game. Just remove her from this mode together with Soraka. You have to pray that the enemy Sona throws the game at some point - 72% Win rate is not just random stuff
