I think she's going to be awesome. She can 1on1 anyone thanks to the sleep-dart making flanks on her harder, she has 200 hp, she can heal at range (probably doesn't matter where you hit, body, head)
She has Ult support, she heals faster than Mercy (which is the worst healer anyway), can deny heals and boost 2nd healer heals.
Her set sounds very good. She'll go well with a Lucio imho, much better than Mercy anyway (I hate it that she's basically a ultimate-only character).