We cut off a BIL too and had to deal with years of hearing about his new wife, job etc from MIL. I bean dipped, DH would stare off and tune her out, I'd bean dip again. We tried everything but MIL just kept circling back to the same topic on every visit.
Since this is DH's mother, I generally let him handle her and I know that this isn't e-Hell approved but.... after yet another recitation of the life and times of BIL, DH looked straight at her and said "I don't care about BIL, he is dead to me. Stop bringing him up in every conversation or you are no longer welcome in my home."
She never brought it up again and she visits even less than before.