Before this meta i'd say at least 21 of the heroes(no joking, i play her a lot) but after this patch you have fewer options if either team is doing double shields lol
Usual counters are winston, reaper, pharah, brigitte(if you can outplay her, if you're gonna keep your shield up she'll just charge on it), and hog, since he can hook combo.
Dive heroes can be good(tracer, genji, dva) but you need to be smart and not fall for the turrets, as they were designed to deal with these heroes(but all of them can escape ther range), for supports, Moira might not be able to kill her but has a nice escape route, if you can hit shots, ana or zen work fine, and baptiste can win the 1v1 because immortality field gives you extra time to try.
If the enemy team has only one barrier hero, any ranged dps counters her as long as you keep your distance.
When playin 1v1s against symmetra your best option is killing her fast, if you got bad aim and your hero can't stun, the using cc/dashes to run is a better option. Symmetra is skinny but she is pretty harmless at long range, as long as you don't get in her beam's range you're good.
Beware of teleporters, if your team is getting destroyed by combos with those use D.va or winston to negate them, they might come with turrets and that technique can be pretty deadly
