I've played her a bit on the test server and she's quite fun. She definitely needs to be on a team that communicates well to be effective.
Her damage and healing are reasonable, but not great. Mobility is terrible, but utility is incredible. The sleep dart can take someone out of a fight for a ridiculous 5 seconds, the heal grenade can negate the healing of the opposing team, and her ultimate (50% damage and HP, and 30% speed increase to a friendly) is a game changer.
Very high skill character.