For anyone that's interested :

I swapped the ECU for another last night and gave it back to my Mom.
I had a chance to acquire a few more OVPs today just in case the ECU doesn't do the trick.

I talked to my Mom more about the failure mode. Always a check engine light accompanied by "chugging." Usually happens at idle but has happened while cruising under light throttle.

I'm starting to wonder about the hoses going to the idle control valve. If (when) the car malfunctions again I'll attempt another OVP swap and have a better look at the ICV hoses.

Gregg