Depends on the scale of the "master plan." But, just throwing it out there, Lucca's home was the site of the duel, and preceding it (or just after it), your forces pretty much razed it to the ground, and Lucca sees you as the general leading that army. Again, egrieved both, but Lucca swallows her feelings and sadness to try and stay aside and say that Elinor was hurt most, and she's just going to duel you for her sake.