My FIL was once an expert user, but has never been able to deal well with any system post-Windows 3.1. He has additional issues as well, but before those grew more severe, we used to be able to handle some of his problems over the phone. (Nowadays I must make house calls, and I usually just fix it myself. But he's only 15 minutes away.)
After way too much trial-and-error, I learned that I had to make sure he was at the computer, and ready to follow some steps and/or answer some questions.
Then I'd say something like: "Let's try this. Here's Step 1." (And then I'd number each step before going into details.) Or, "I'm going to ask you some questions. First question ..."
Whenever I moved too quickly into Solution Mode and forgot to ease him into the process of actually doing something, all we got was confusion. His way of handling confusion was different from your Mom's, but the result was the same -- Problem Unsolved.
I have no idea if that's what's happening with your Mom, but if she's not prepped, then she may simply not be hearing your first instructions. So, by the time she finally does tune in, she's thoroughly lost.
If she hates to make phone calls and chat, then the simple but stressful effort of making a call may be yet another distraction. Double brain-freeze!
As others have said, your only recourse may be to refer to the already-written notes, broken-record style. (You may also want to ask her if the notes give her trouble, for any reason. And always keep copies of the latest version handy for yourself.)