The Question and Answer section for Romeo and Juliet is a great resource to ask questions, find answers, and discuss the novel.
In essence, Juliet is blushing because Romeo has heard her words, but she won't deny them because she's more concerned with his feelings than her own manners.
Juliet claims the nightingale is still singing because she doesn't want Romeo to leave, as the nighingale only sings at night.
Capulet tells his wife to prepare Juliet for her wedding.
Prepare her, wife, against this wedding day.—