Tyrande should be there not because she wants to help the Alliance or not because she is following the Horde to end them. She should be there because she knows first hand the danger Azshara is. She has witnessed the horrors that woman can unleash and how night elves and herself are usually the targets or Azshara’s rage.
Tyrande’s presence there should be more in the lines of this:
Tyrande: I’m here only to put an end to Azshara’s raign of horror and to avange every kaldorei who did not survive the sundering.
Jaina: We must put aside our hatred and work with the horde for now in order to stop Azshara once and for all.
Tyrande: Foolish child. Trust them at your own risk. For the time being them more of them that dies at the hand of Azshara the less my people will.
Thalyssra: We have all being wronged by our former Queen. We must stand together as we did before if we are to face her again.
Tyrande: I have Azshara on my sight right now but don’t think for a second I won’t come after the horde the moment this is over. You can use this time to think where you want to be when I turn my gaze upon the Banshee Queen and all who would stand beside her.
Put some sass on Thally and Lor’themar or whatever and there you have it.