You dumb or what. An ally + herself = 2. You are always taking damage on Sona since you are on the frontline poking with Q.
You are arguing with a 3K games aram player with a 2K elo rating. Just saying.
She builds full AP, a luxury other contenders can't do. Her shield triggers the armor/magic resistance buff on 4 ppl. On Aram every player is near eachother, you shield everyone all the time, the aura lasts several seconds it's enough to shield everyone. She shields 5 ppl and heals 2, she does it all the time she often builds a tear, and has near max cdr, thanks to new chalice that is cheap as hell. On that note, she is the best champion to make use of the new chalice as well for even more healing, since she has an easy time poking and doing damage with Q.
Edit, I'll bring some numbers too, since you can't read nor math.
http://leagueoflegends.wikia.com/wiki/Sona/Abilities
http://leagueoflegends.wikia.com/wiki/Taric/Abilities
Sona 「 MINIMUM HEAL: 30 / 50 / 70 / 90 / 110 (+ 20% AP) 」+ increased by 0.5% for every 1% of target's missing health + SHIELD STRENGTH: 35 / 55 / 75 / 95 / 115 (+ 20% AP) (+ 10 / 20 / 40)
Taric HEAL PER CHARGE: 20 / 30 / 40 / 50 / 60 (+ 20% AP) (+ 1.5% bonus health) (not counting the charge system that is useless since you spam heals anyway)
Sona shields twice more than taric heals, and she also heals and she heals more and no healing is wasted ever unlike Tarics heal, and she heals more often and her heal/shield is easier to apply.