Ask yourself these questions ... "What do I want her to know about me?" "What is it about me that will help me get this job?" Those are the things you should include in your answer.
A lot of personal stuff is irrelevant (how many kids, hobbies, etc.) -- so don't waste time talking about that type of stuff. In fact, that general question is one way that applicants can hurt themselves by divulging too much about their personal lives. There are a lot of personal questions that interviewers are not allowed to ask -- but if the candidate brings it up herself in the interview, then it can be used against you in the selection process. For example, "I just got married and my husband and I want to have lots of kids right away," tells the interviewer that you will be taking lots of time off in the near future and may not be the best applicant for them to hire.
Focus on the information relevant to the job. I would start by giving a basic introduction, "I have worked as an aid here on ___ unit for ___ years while going to nurisng school. I recently graduated and I hope to get my first RN position here because ____. I am particularly interested in ____ patients and I find the _____ aspect of nursing to be particularly satisfying. I think this job would give me the opportunity to do that kind of nursing and to continue to develop my nursing skills in that area. What else would you like to know?"