What does the bright red MGB Roadster represent to Susan in the novel, Moonflower Murders?

At the beginning of the novel, Susan mourns the loss of her old life as an editor and owner of her own publishing company. She feels she is escaping back to her old self when she is given the opportunity to go back to England to help Lawrence and Pauline find their daughter. Among the first things she does is to get the roadster she bought for herself as a fortieth birthday gift out of storage. When she drives it, she feels as if she has some of her old independence back.