。
She must be angry.
Literal
She [topic-は] angry [must be-にちがいない].
~に違いない expresses strong inference — the speaker is virtually certain. 怒っている ('is angry,' ongoing state) + にちがいない = 'she must be angry (I'm sure of it).' Stronger than ~だろう (probably) or ~かもしれない (might), this pattern leaves little room for doubt.