I'm in higher ed and I do think you are correct in this situation. I would never ask a departmental admin to handle my personal financial documents unless it was part of some process only that person could complete. She should be more concerned about protecting her own privacy, in addition to the issues of wasting your time. And really a person with a Ph.D. on a college campus should be able to find a scanner and use it. I think that many academics have trouble understanding that an AA who works for ten people is not the same as a personal assistant.
The bigger issue of where to draw the line is really tricky. You don't want to get a reputation for being fussy and unhelpful and it can certainly help your career to be perceived as flexible. However, if you say yes to everything you will get stuck parking cars, walking dogs, babysitting, buying coffee, getting dry cleaning, and helping professors' kids with their homework (these are all things that I have seen personally). In your case, I would try to be pleasant but firm with the people who step over the line, and super nice and helpful to the people who are aware of boundaries. If you do that you should have some good allies in the department if the line steppers start complaining.