Question

… her relief, nobody had seen her
A) To
B) In
C) For

Answer 1

A) To

The correct preposition in this sentence is "to": "To her relief, nobody had seen her." The phrase "to her relief" means that she was relieved or happy about something. In this case, she was relieved that nobody had seen her. The preposition "to" is used here to indicate the person or thing that is affected by the feeling of relief

Answer 2

To her relief, nobody had seen her