What's so bad about that ship that would make Uhura so angry about being assigned to it?
We don't know this of course, but perhaps her
main reason for wanting to be on the Enterprise was not because of it's status, but because her boyfriend was first officer?
Perhaps, if Spock was assigned to the Farragut, that is where she would have wanted to be assigned.
We'll never know, since that's not how the movie plays out. And Uhura is certainly a capable Starfleet officer looking for a distinguished career, not just a fangirl of a dreamy half-Vulcan. But humans often give relationships top priority in career choices; if she is in love with him, it would be quite reasonable for her to do so as well.