She forced Nathanos, the acting general of Darkshore, to flee and killed one of Sylvanas' val'kyr (Brynja). She also led the taking of Bashal'aran, which served as the base of Kaldorei operations on the warfront. Not to mention slaughtering the majority of Belmont's standing forces in Darkshore. Keeping the Jailer occupied on his home turf by killing tons of his minions definitely helped. After destroying the Amalgam, Tyrande left to continue the hunt for Sylvanas and the PC hovered up the remaining Kaldorei souls into their soulkeeper and returned to them to Ardenweald, as per "Stage 11: Salvation of the Night Elves" of the quest-chain "The Recovery of Tyrande Whisperwind." Defeating Sylvanas isn't a requirement for actions occurring or having an impact, and in slaying a ton of Mawsworn and occupying Sylvanas, she saves many Night Fae lives (existences?) in the process, despite Sylvanas escaping.