I think it should be: She got the better half of the deal and I got the worse half. Anyway, I am interested in this question too, because I was thinking that maybe native speakers could also say: She got the best half of the deal and I got the worst. Now, I know that "best" and superlatives in general are also used when there are only two items, but I wonder if in "the better/best half of something", one or the other could be some kind of idiomatic collocation.
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