Mom’s thought process & memory getting worse & conversations making less sense. What can be done?

I agree with @97yroldmom start with the basic visits to the doctor for a full check up. Ask doc to take a look at any meds she's taking, do the blood work, check for urinary tract infections etc. Then move on the the Neurologist if the medical doctor gives the all clear. It's scary when someone we love seems to be slipping away but at least knowing why can help a bit.

What have you done so far? Has she been to her primary for a checkup and a neurologist for cognitive testing?
Start with the basics.