、。
She thought, 'I hope Mother won't be angry.'
Literal
Mother [subject-が] get-angry-[conditional-なければ] good [but-が], [quotative-と] she [topic-は] thought
怒らなければいいが = 'if (she) doesn't get angry, it would be good, but...' — ~なければいい expresses a hope that something won't happen. The trailing が adds a note of uncertainty or worry. と marks the preceding clause as thought/speech.