Well, if 1-2" from the wall is her only requirement and she didn't mention anything about how much total space the sub was allowed to take up; then I have an idea.

Pick out a massive sub...something a good 6-8" or more deeper and/or wider than the PB-12 and tell her it's the sub you plan on purchasing. Then, using its measurements, take her along with you and measure the corner space the sub will take up factoring in her 1-2" wall requirement.

After that, inform her that you might be willing to compromise by purchasing a smaller sub (PB-12) that requires 4" placement from the walls, but will still occupy less floor space than the other. Maybe she will come to realize that the amount of total space the sub will take up is more of a factor than how far it is placed from the wall. It's worth a shot.