I mean at least before, Angela brought her on to be her secretary when she started the Bower Agency? Is it safe to assume that Mona never worked an actual 9 to 5 job in her life before that? I read that she even said so somewhere in Season 2.

Others have said that maybe (https://www.reddit.com/r/WhosTheBossSitcom/comments/1b4gfw4/im_so_glad_i_can_watch_this_from_start_to_finish/) Mr. Robinson (Angela's father) left Mona a lot of money. It has after-all, been implied that Angela grew up wealthy and Mona therefore, married rich.

Yeah I was never clear on this either, also in the earlier seasons wasn't she in school studying psychology? Then they never talked about that again really.