No, she's correct, but the question may not be well-formed.
"a.m." and "p.m." as instructions would have a "q" in front of them. They all stand for Latin words, not English ones. The "q" is for "quod" and "q. a.m." literally means "quod ante meridian," that is, "each morning." "Q pm" similarly means each afternoon.
In the abbreviation '"a.u." the "a" is for Latin "auris" = English "ear." AD is aurum dexter = right ear; AS is aurum sinister = left ear; AU is both ears. (I'm sorry but I don't know what the U expands to in Latin.) Similar considerations apply to OD, OS, and OU where O = oculus = eye.
Incidentally it is now considered that those six abbreviations should be avoided because they are open to misinterpretation. Doctors' are notorious for having bad handwriting, and every so often an "o.d." is misread as a "q.d." ("quod die" = once daily); and worse, the period is read as an "i" and the abbreviation is misread as "qid" = "quart. in die" = "four times a day," and the patient gets a large overdose by the wrong route. It doesn't happen often, but a small percent of millions and millions of prescriptions is a significant number, even if it's a very small rate.
"A.P." is an abbreviation I was never taught and never heard of; "as prescribed" is as good a meaning as any, but it's not universal. When I can't be specific about what the dose will be because it changes frequently, or the instructions would be too long to fit on a label, what I've written is "U D," for 'ut dict.", meaning "as directed."
I'll remember A.P. If the pharmacist doesn't know it he/she'll call and ask what I meant.
