Will Allah forgive the questioner for not dealing with her maternal aunt, and does this maternal aunt fall under the category of "maintaining kinship ties" (silat al-rahim)?

Your aunt's relationship with your father is illegitimate and forbidden, and she must repent. Your inheritance from your father is not forfeited by this relationship or by his marriage to her. It is recommended to maintain kinship ties even if the relative is a transgressor, as evidenced by Asma bint Abi Bakr's maintaining ties with her polytheist mother. A disobedient Muslim is even more deserving of maintaining ties.