。
She might not come to tonight's party.
Literal
She [topic-は] tonight 's party [to-に] [topic/contrast-は] not-come [might-かもしれない].
The compound には is a particle stack: directional に marks 'to the party,' and contrastive は draws an implicit contrast — she might skip this one even if she usually attends, or she might miss this party while still going to others. Stacked particles like this are hugely productive: にも, でも, とは, からは all carry similar layered meaning. かもしれない softens the negative prediction; in casual speech it commonly contracts to かも.