Love her design. When reading her abilities it sounds OP but in game It's surprisingly balanced.
I love that she can't crit-shot or deal massive damage. 80 damage is pretty good, she's a support first and supports shouldn't be killing as much as healing. It's good that she won't be able to easily outshine a widowmaker as her more versatile kit would make widowmaker obsolete if that were the case.
80 points of near instant healing administered from long ranges. It's not a constant supply of health like the others, but it's enough to save somebody in the heat of the battle (essentially a long-range health pack). Again I find this to be good, as she shouldn't outheal The others consistently but rather she should be able to easily save peop when need-be.
Her grenade is a godsend, especially if you combine it with a Lucio or mercy healing the whole team. It will also make pushing objectives easier as you could shut down the enemy healers for a short time. Sleep dart similarly is a great tool, but requires good coordination to use effectively.
All in all, I find her to actually be incredibly balanced, and I love how she is so far changing the meta up. She require a a bit more skill to use effectively, but in the right hands, with good team coordination, she's a great addition.