She was an utility Support. IMO, Sombra also fit that, but for some reason the devs preferred to stick her into the Offense role. I still believe the general reaction to both Sombra and Symmetra would be better if they both were simply categorized as non-healing supports.
I think she can work if the devs just try out a mechanical change to shields to make them counter high-damage bursts in the same way armor counter chip damage. I go into details here, but that alone would skyrocket Sym and Zen viability (immunity from sniper shots), and if Sym go back into granting shields, she can also shield an ally against sniper shots as well.
They need to look back at shields in general, and return Sym to her original role as the shield-granting support.