Rebecca Nurse is the quintessential puritan personality. Most people would describe a stereotypical puritan as patient, kind, loving, caring, slow to anger, pious, giving, etc. Those all describe Rebecca Nurse.
She is also a woman that is not prone to immediate panic or hysteria. That's evidenced when Rebecca sits down next to Betty who has been making odd noises and can't seem to settle down in bed. Rebecca sits on the bed, and Betty is calmed. When asked what she thinks is wrong with Betty, Rebecca replies that she believes that Betty will tire of her antics and be back to normal shortly. She believes this based on her own personal experience as a mother and grandmother.
Rebecca, sitting: I think she'll wake in time. Pray calm your-selves. I have eleven children, and I am twenty-six times a grandma, and I have seen them all through their silly seasons, and when it come on them they will run the Devil bowlegged keeping up with their mischief. I think she'll wake when she tires of it. A child's spirit is like a child, you can never catch it by running after it; you must stand still, and, for love, it will soon itself come back.
Another piece of evidence that shows that she is not a person prone to hysteria occurs when she tells Parris to send Hale back. She is worried (correctly) that Hale's presence will cause more panic than is already in the town of Salem. Rebecca advises instead that the town turns to God in prayer. This shows that she isn't only a confessing Christian, but a practicing Christian that believes in the power of prayer and God.
Rebecca Nurse is proper and "common sensical" in the opening act of the play. She counsels against invited Reverend Hale to Salem to investigate the possibility of witchcraft, correctly pointing out that existing schisms and enmity in the town will simply be re-ignited by an outsider.
When Proctor sides with a hypothetical devil against Reverend Parris, Rebecca tries to get John to take back his words. She is concerned with not only seeming Christian, but in actively following a code of conduct, demeanor and speech that she sees as definitively pious and Christian.
This sets her apart from certain characters like Reverend Parris and John Proctor. This also demonstrates her concern for others (and the souls of others), which, again, separates her from Reverend Parris who is quick to condemn others despite his great piety.