I like what Pete Zahut said-JWs love to think of Jehovah as a reader of hearts. It brings them comfort to think that no matter what, he knows their true motive and understands their human frailties.
Tell her that Jehovah undoubtedly understands how conflicted she is and undoubtedly appreciates her taking the matter seriously and being respectful enough to withhold from partaking from the emblems when she’s not all together sure.
& TTWSYF's It's great that you have even reached out to this lonely elderly woman. Just giving her your time is showing great love.
I think considering her age simply telling her that jehovah is the reader of hearts , combined with just listening to her (giving her your time) will do wonders. I would ask about other things that are important to her or things she likes. Make idol chit chat. Let her know that your there for her if she needs someone to talk to. That will do wonders.
My Great Grandmother was pulled into the borg when she was 75 by her daughter. She got baptized and then disfellowshiped at 78, for being a 'slut'. LMAO.(actually not very funny) She had Alzheimer's and Dementia and would frequently have guys over to help her with fixing things. So someone saw it and turned her in. Dfed, as she got violent(dementia) and was unrepentant(she did nothing wrong). And it made the old age declining mental health problems way worse. I loath those probably now dead elders and my bio fam for doing that to her. I spent lots of time with her even when she was dfd and she simply adored the company. And I enjoyed listening to what she shared about her life.
My point to that is at her age 88, I would let her lead the conversation and just be there with a listening ear. She's lonely, a little hurt and scared. Just needs a person to talk to. Keep it up beat as possible. In this case I wouldn't bring up anything contrary to her beliefs. Sometimes the greater sacrifice or way to show love is keeping our mouth shut when we want to scream. I feel for her.And for you.
Good luck.