Lady Falconbridge makes a brief appearance at the end of Act I, Scene 1, where she shows up to challenge all the horrible rumors that have been spread about her. When her son Philip the Bastard tells her that the gig is up and that everyone knows she slept with Richard the Lionheart, Lady Falconbridge admits it—though she protests that she had no choice in the matter.
Does this mean that she was raped? It's not entirely clear. The hint seems to be more that Lady Falconbridge was seduced by Richard, and thus "couldn't resist" his charms. But you can argue either way.