That's exactly why bylaws are there--to deal with issues like this. Is your principal an officer of the PTO? Are you independent of the school? Why does she get to decide whether you have to follow your bylaws?
If your bylaws are really that outdated, then maybe they just don't work very well for your organization now and should be rewritten. Maybe you could set up a bylaws review committee and have them come up with a revised set of bylaws and have the membership vote on changing them so they work better for your organization.
Your bylaws most likely had to be filed with the IRS when you applied for tax exemption. But it's not like the IRS is going to come after you if you aren't following them. If you're doing something outside of the scope of your stated mission, then that is more likely to jeopardize your status. But even then, someone would need to complain to get a review going, and the IRS only has limited resources.
Our PTO officers are not agreeing on most issues. I have referenced our very outdated bylaws on numerous occasion to try to deal with this issues (basically call to vote). Our principal informed me that we do not follow the by laws and we haven't for years. Is this a potential issue for our 501c3 status? Is there anything to deal with this very frustrating issue?
