Playing Ana as a solo healer is tough even with good aim unless people know to stay in your sight lines if they need heals (which almost definitely they don't).
I said it the other day that i think since she is so aim centric with her support ability, that she doesn't have a good chance of becoming meta or a viable comp at high levels consistently. Even great aimers can miss shit in the middle of action with everyone moving around. I would prefer just having Zen being able to fling his healing plus the discord ability.