。
She didn't put up with his selfishness.
Literal
She [topic-は] his [genitive-の] selfishness [object-を] didn't-allow.
わがまま ('selfish, willful, demanding') is one of the most useful Japanese words for capturing childish or self-centered behavior — applies to children throwing tantrums, adults insisting on their preferences, partners being demanding. Both noun and na-adjective; here used as a noun (object of 許す). 許す ('to forgive, allow, permit') is multipurpose — context narrows here to 'allow, tolerate.'