The Nightborne didnt respond badly until after Tyrande had spat in their face. If I remember right a few times.The Nightborne are, as is in theme with their entire culture, ungrateful. In their eyes, the Alliance -- who did a lot more than the blood elves -- did so out of obligation for their own needs, not for them specifically as they feel the blood elves did (and whether or not they did primarily for the nightborne remains to be seen... it's doubtful).
I think Tyrande's character needs work but this scene doesn't really make me feel like she's a terrible person. I thought the story had occurred in person, but in the quest, it's a comment that was made before they conquered the Nighthold. Whether or not it was for selfish reasons, they played a major role in freeing their people, and the nightborne responded with apathy since in one special case the night elves were slightly unfriendly to them.
At first I was really upset about Tyrande, but once I saw the context, it's actually Thalyssra I'm bugged by. She is being portrayed as a rather shallow character, but perhaps this is what she always was. The only character I am bugged by is Alleria, because she portrayed the diplomatic prowess of a gnoll in that same scenario. She should know better.