>>>First, you didn't mention if you are prestige, elite or super elite [SWU does not give much detail, only can rule out you are not aeroplan basic]

I am Elite.

>>> Second, for your departure flight, it seems first row of 161 is occupied/assigned so that can be another reason she said no.

I see. I was only told, very rudely, that she could not assign those seats.

>>> Third, why don't you "pre-assign" your seats when you book your ticket?

I purchase my ticket via a travel agent, instead of Air Canada. Therefore, have to call for seat assignment.