Sorry, what does "OP" mean? *confused*
I don't know. The Queen of the Elves, in previous books, was self-centred and malevolent with no possibility of allying with anyone. So once she gets kicked out of Fairyland, she has no chance. Terry's basically painted himself into a corner. The Queen might as well die, but Tiffany needed allies against Peaseblossom. Perhaps that's why they were allied? An alliance of convenience?
If this how it would've been written, it would be easier to figure it out:
TIFFANY: We have been enemies, but it is in both our interests to see that Peaseblossom is removed from power.
QUEEN: Such as alliance is in my interest, small human. Very well. But once I am in power again, our alliance must be dissolved.
TIFFANY: Agreed. (They shake on it)
This is more believable than Tiffany and the Queen becoming "friends", I guess. But once the Queen has been kicked out of Fairyland and mortally wounded, I really can't see her acting this imperious. Wouldn't you agree?
If this how it would've been written, it would be easier to figure it out:
TIFFANY: We have been enemies, but it is in both our interests to see that Peaseblossom is removed from power.
QUEEN: Such as alliance is in my interest, small human. Very well. But once I am in power again, our alliance must be dissolved.
TIFFANY: Agreed. (They shake on it)
This is more believable than Tiffany and the Queen becoming "friends", I guess. But once the Queen has been kicked out of Fairyland and mortally wounded, I really can't see her acting this imperious. Wouldn't you agree?
And, of course, we also see the difference between the members of the New Firm. Mr Pin doesn't feel remotely sorry for his crimes, and so is reborn as a potato, ready to be fried. Mr Tulip has at least enough belief and a desire to redeem himself, so he's reborn as a woodworm nomming on antiques. The latter has a chance to potentially redeem himself eventually.
Good redemption arcs tend to be long ones. The epiphany may be instantaneous (though it isn't always), but the road to redemption is a long one, maybe neverending. Jaime Lannister, Kiritsugu Emiya, Mike Yates, Farnese di Vandimion, Miranda Lawson, these are characters with decent redemption arcs in fiction. Actually, whether redemption is instantaneous or ongoing is a central theme to the game Bioshock Infinite.
I must emphasise, this does not mean The Shepherd's Crown isn't a good book. It's still quite a good book, and it's definitely Terry Pratchett's loving swansong to his readers. But it had a number of faults for me, and Nightshade's so-called redemption was one of the notable ones. IMO, it would've worked better if she was overthrown at the start of the book, rather than about halfway through, more or less. That would give time for a proper redemption arc.