Feel very disrespected by Administrator

I'm the Director of Nursing of an outpatient dialysis clinic. While I was off 2 days, the administrative assistant really dropped the ball and sent some very unfinished re-assessments to the Doctor.(note my secretary and my administrator are buddy-buddy and her behind the scene snitch so to speak). These were not going to be used and had been sitting in a back office since November pending the administratos instructions of when to implement thier use. Of course the Dr was angry he recieved about 20 to complete and wasnt aware he shouldnt have recieved them. Bless his heart he did every one of them in less than 24 hours! I had absolutely no knowledge of the incident until I got a nasty email from my administrator (her home office is in another clinic). She demanded I come in at 6am and was to have them all completed no later than 12pm that same afternoon. Also due to lack of licensed staff I have been working the floor 6 days/wk, 12hr days as the only RN staffing the floor in addition to my management responsibilites!!! Dr. completed his end now I must due to state inspectors most likely coming in so we have no choice but to use them.(The nursing section is 4 pages long including a careplan to it). Once I found out what was going on I stated to her "I understand the situation and wished you had called me at home as I had no knowledge of incident therefore was in the dark regarding your email until I spoke with the secretary. Rather than pointing blame we should be working on a solution" (Keep in mind folks, the secretary denied doing this and she is the only one that takes any files for completion to his office.) The response my administrator gave me was " I'm the Boss and I can say what ever I like when I like!" Needless to say I was floored as her manner was just very nasty and disrespectful. I had already been in and had over 1/2 of them completed before she came down to the clinic. I had no problem doing them as I felt as a manager the damage was done so work together to resolve it and get the paperwork done. So that wasnt an issue for me. I've been in nursing for 30 years and held some major administrative positions myself compared to this little clinic and I would never have spoken to one of my staff like that. I would never permit one of my charges to talk like that to any one they were responsible to supervise. Needless to say soon as she said this I gave a 30 day notice I am stepping down as her DON. Now she cant understand why I'm stepping down. How should I have reacted to her response? This wasnt she was just having a bad day deal. Last week she had sent an email to me regarding getting ready for state but didnt realize she had attached to it a previous email to the secretary stating "this should really set "So-So" off, LOL". It inadvertantly came not only to my email but 2 other peoples accidently!!!! Keep in mind these other staff members along with the Secretary are under my supervison in the clinic. I felt very belittled by it. I understand now she has treated staff like this long before me and was advised by others to just "take it" and not say anything. She has been unable to keep staff. Apparently she has been treating people like this for years. What would you have suggested as the best way to have responded to her? I'm a pretty tough cookie but I refuse to be verbally abused or disrespected by anyone, including the administrator. This is a position I wasnt hired for but drafted to when she fired the last DON. I also think it's very unappropriate for her to be discussing and making statements to someone I am responsible to supervise as it undermines my position. Any advice, I love my patients and my staff and dont really want to go but I cant work for someone who can disrespect me or others that easilly. Plus I cant work any harder than I have been and I'm salary. So working 50-60 hours then to be treated like this? Bye bye is all I could say.