Just had this convo with my brother (an elementary principal) the other day. People to keep happy if you're involved in PTO, and in this order: School Secretary, Head Custodian, Principal. That was the order that he, as principal, put it in. He said he'd add cafeteria staff - but ours is outsourced and we can't use any of their stuff anyway.
My suggestion, however, from experience with this type of admin assist, is that if you think she is acting as a blockade between you and principal on an important issue, and if you think it is not policy but ego getting between you and the door to his/her office - call and ask for voice mail for the principal when you know he's not in. Leave a vague message asking to have your call returned and then discuss with him/her or make and appointment when you will have his/her undivided attention. Ask your question in some other wording so that it is not the SAME question. This way you have not stepped on toes, you have not gone "over the head" of the admin, it was something new that came up that you wanted to discuss.
YIKES - from reading some of these posts about having to fill out a form to talk to the principal, or fill out a form in order to fill out a form, almost makes me glad I don't WORK at the school (or do I?)
Finally - if your PTO has sufficient supporters that you can offer someone to work in the office an hour or two every day, to cover lunch breaks, especially busy periods, or whatever, I am pretty sure that might help pave the way to better communication between the PTO and the office staff. At our middle school of 1800 people, the PTO covers the attendance office for 2 hours a day, in the morning, helping get the tardy slips written, re-admit slips for students who have been absent, and "leaving early" slips. When we do the "what is your special talent" form at the beginning of the year, one of the options is "office help". Can't tell you how much it means to the attendance clerk, and more importantly to the others who cover her job if she is late/sick/out - that someone else knows what to do and is there to help. Gets us many favors in the bank for doing this, and well worth it.