I guess it depends on whether the pool owner is going to followTFP methods (based on current science) or the PB 1980's methods based on "we've always done it that way".
Stabilizer (CYA) needs to be added either way. A CYA of "0" makes the chlorine very harsh and the chlorine will also burn off quite fast.
In either case, you aren't going to win with the PB based on the data that has been provided to them.
Doing another acid wash will shorten the life of the plaster surface.
Get the pool owner to register on the forum and get them to obtain a proper test kit.
Test Kits Compared
If this is a SWG pool, the TF-Pro Salt is the best bang for the buck.
Let us know what the pool owner decides.