Yea, but why did she have to kill off Tonks? That I don’t understand... besides plot expediency?
She didn’t “have to” kill Hedwig, or Fred, or Colin Creevey, or blahblahblah ... only really “had to” kill Voldemort.
My view on Tonks dying was that she was going to follow Lupin no matter where he went or what he did.
In an earlier book she left her “post” unguarded to find out if Lupin was alright. That is why she was wandering the halls in Hogwarts when Harry ran into her.
Then she again left her “post” which this time would have been her obligation to stay alive for the sake of their new baby to follow Lupin into the fight.
It seems to me her highest priority had always been Lupin, so it made sense if he died, she would die also.
Maybe?
There's no real expediency to killing her off -- Rowling killed them off for a reason. Lupin, in going to war, was doing what men have always done.
Tonks is essentially a soldier, too -- and her choice is more complicated. Does she stay home with her kid, relying on Lupin and everybody else? Or does she, too, fight, so that even if she dies, her child will grow up free from Voldemort's control -- either that, or die trying?
That's a very tough choice to make, and Rowling sets out the worst possible result. The question we have to answer is: did Tonks choose right? Why or why not?