Jane loses her virginity in Chapter Forty-Seven.
According to the reference:
Until “Chapter Forty-Seven.” This episode — directed by Eva Longoria! — had a hell of a job. This was the episode in which Jane was set to lose her virginity, rendering both her past identity and the show's title moot.06-Nov-2016
Therefore, "Chapter Forty-Seven" is the specific episode where Jane loses her virginity.
