She sounds like she's a classic NPD person, to me... and with that, NOTHING can be done. NOTHING you say will change that and the further you try to engage and EXPLAIN the crazier you'll get about it. You are feeding her supply as long as you engage about it. It's has nothing about her really feeling that way about him and it has everything to do with her knowing how to get your goat. I understand that she's in her 70's and it would cause more drama to go NC, so I recommend putting in a VERY FIRM BOUNDARY that none of this is up for discussion (and it's really none of her business!!). Oh sure, she'll find other ways to try and engage to get your goat (or just ignore you and keep on about HIM)... but it's up to you on staying firm of YOUR boundary you put in place and you will not engage (e.g. feed her the supply she seeks). She may eventually get tired of playing her NPD game and move on to the next victim. Good luck.