Mildred's reaction to the revelation of her suicide attempt is one of complete denial. She tries to kill herself with an overdose of sleeping pills, but when she comes round the next morning she claims to have no recollection of ever having taking any. Despite Montag's attempts to make her face up to the truth, Mildred doubles down on her denials, insisting that she wouldn't try to kill herself in a billion years.
This is pretty typical behavior for Mildred. She's the perfect representative of a society in which people are encouraged to hide their true feelings and pretend that everything's just peachy when it really isn't. In this book-hating society, everyone's expected to lose themselves in mindless, escapist entertainment, which is supposed to make them happy. But as we can see with Mildred, that isn't always the case.