If this were to happen in a story, society's response would vary greatly. In some modern and progressive communities, people would likely approach it with an open mind, understanding that sexual orientation can be a complex and evolving aspect of a person's identity. However, in less accepting areas, there could be a lot of judgment. People might gossip, and she could face exclusion or even be pressured further to continue in a heterosexual - acting relationship. There would also be those who would use it as an example to reinforce their own narrow views on sexual orientation.
Society's reaction would likely be mixed. Some might see it as a sign that she was never really a lesbian in the first place. Others might view it as a form of her trying to conform to the dominant heterosexual norms. In more conservative parts of society, they may simply condemn any deviation from what they consider the 'right' way of living.