Professor Miller should give Olga a chance to explain before assuming lack of motivation. It is not uncommon for foreign (and sometimes U.S.) students to be uncomfortable discussing personal issues with persons in authority, such as the students research professor. Olga and her husband are in the midst of a separation; Olga has every intention of completing her degree requirements, but her family problems are preventing her from concentrating.
Professor Miller decides to call Olga for a meeting to discuss just this issue, without focusing on research results. When asked directly if there is a problem, Olga reveals her marital troubles and tells Professor Miller she will need a few weeks to deal with them before she can return to the lab. Professor Miller offers moral support and understanding and is willing to accept a delay in obtaining results. Olga does resume working after a couple of weeks and finishes her degree within the expected time period. She is grateful to her mentor for being understanding and supportive.