Can my daughter (a nurse) be my health care agent in my proxy?

No, your daughter can be your health care agent.  Massachusetts General Laws Chapter 201D, Section 3 says: "No person who is an operator, administrator or employee of a facility may be appointed as health care agent by an adult, who, at the time of executing the health care proxy is a patient or resident of such facility or has applied for admission to such facility unless said operator, administrator or employee is related to the principal by blood, marriage or adoption."

Based on that language, you may certainly name your daughter as your health care agent.  Also, you could name other nurses or doctors as your agent, as long as they do not work at a medical facility where you are, or may become, a patient.  Hope that helps.