Mom Not eating?

Hi there,
Mom is 84, widowed, and she doesn't eat. No breakfast, Maybe a handful of animal crackers with her 3 cups of coffee.
if she does eat, it's around 1:00 in the afternoon, and that's dinner.
most times, she lives off of 2 cups of fruit jello and junk food, like chips, slim jims.
there are days she doesn't eat any meals. 'she's tired of eating the same foods, everything tastes funny ( it was like this before Covid ever happened), she forgot or she's not hungry'. She doesn't cook anything, so IF she eats, it's frozen dinners, which I'm ok with.
I've tried explaining to her that she's doing more harm than good.
I ask her every day if she's eaten, and I know she lies to me, because my brother and myself are getting on her about it.
I'm at wit's end, and need some advice!
please and thank you in advance!