Want to know if my sister needs a lawyer before answering police questions.

Detective came to her house, spoke to her mother and daughter while she was at work. He had her correct car make, model and license but wrong car color. Stated that an eyewitness gave the information related to a theft of copper wire at an apartment building. She is completely innocent, was visiting a patient at the time (she is a nurse who makes house calls). She called and the sheriff department detective asked her to some and answer questions. She is en route with her work log for recent weeks. Does she need a lawyer or should she answer questions, considering that she is completely innocent?