How can I reconcile lowering my gaze with sitting among foreign women, especially since my father considers my avoidance of them to be reclusiveness, citing the presence of women in the gatherings and battles of the Prophet, peace and blessings be upon him?

You are correct in avoiding sitting with a non-mahram woman, because the temptation of women is among the greatest temptations, and isolation in such a situation is not blameworthy. The participation of women in fighting alongside the Prophet, peace and blessings be upon him, was within the bounds of Islamic etiquette, with hijab and without unlawful mixing. Apologize respectfully to your father if he invites you to sit with her, and do not obey him in what displeases Allah, for "there is no obedience in disobedience to Allah; obedience is only in what is good."