I say she kinda gained some depth in character with that. As >>74
stated she otherwise is somewhat plain, like an over-polished surface with no hook to get a hold on.
With the sudden change of events, her whole prior behavior suddenly seemed intricate and scheming, playing the nice girl while plotting the ultimate deceit. Bad ass Manami is fucking devastating.
Her development is comparable to that of Miki Sayaka in Puella Magi Madoka Magica Rebellion. The whole series she was an (citing her) idiot, but with the third movie her position unexpectedly jumped over that of Homura, giving her that hard-boiled been-there-done-that side.