She watches his body burn and she thinks of all he took from her, but she also thinks of all he gave her —- the life of a Grisha, being accepted and embraced by people like her, the courage and determination to use her power, to oppose him (but there was always the hope, infinitesimal though it was, that he might join her).

She has given up her power for this moment, and in killing him, took his from him.

But she is familiar with this power, this loss, with merzost, and she knows that the making at the heart of the world is never truly gone from her — her powers will return and so will he, and it’s just a question of which will be first.