She's not gonna show.
She's not gonna show up.
She's not gonna come.
Are these completely interchangeable?
They mean more or less the same. "show" and "show up" are somewhat informal in this sense, while "come" can be used at any level of formality, but this difference is obscured because the flavour of your sentences is dominated by "gonna". "gonna" is a low-grade contraction that you should use only when you deliberately want to impart a very casual flavour to your writing.
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They mean more or less the same. "show" and "show up" are somewhat informal in this sense, while "come" can be used at any level of formality, but this difference is obscured because the flavour of your sentences is dominated by "gonna". "gonna" is a low-grade contraction that you should use only when you deliberately want to impart a very casual flavour to your writing.
People learning English should be aware that "gonna" is not really a word, and no literate native writer ever uses it outside dialogue without the intention of lending a coarse or childish tone to the voice of the piece.