whoa!
Here are my initial thoughts--if everyone else likes this person, what's your reason not to like her? If you sit five feet away from her, have you sat there in silence the whole time you're worked together, or do you have some kind of relationship established with her? If you want to keep the job you have, and if the owner has ordained her as your supervisor, then it's in your interest to figure out how to make that work for you. If it was me, I would e-mail you requests, because it's good managemet to put work requests in writing. You have a paper trail that way, as a double-check on information, as a reminder, etc. So why are you bristling at her sending you things in writing? That's just good management, in my opinion.
You say "apparently" she has been given complete authority over you--you don't for sure? Nobody has discussed this with you? If not, you need to ask your business owner, or whoever has been your supervisor up till now if the reporting hierarchy has changed. Don't get pissed off--ASK!
I'm not sure what you expected with this job, but unless you start your own business, you will spend your time being someone's ***** (whatever those "stars" stand for). So figure out what you like to do and get GOOD at it, so you can be higher up on the food chain. You will always report to someone, though, so just get used to that idea.
If you are serious about finding a new job, I wouldn't tell your boss. If it was me, again, I would just pay you through the end of the pay period and let you go right away, esp. with you having access to computer systems, etc. Disgruntled employees are security risks in small and large ways, so a lot of companies just escort someone out with a box of their personal belongings, once they tell the boss they are pissed off about something and thinking about quitting.
If you do change jobs, learn from this experience and don't take a job that does not have a title and a clear job description, including duties, some kind of plan for advancement (including what you need to do to earn raises, annual bonsues, etc.) who supervises you, etc. That way, if something does change at work like the situation you're describing, you at least have that as a prior agreement between you and your boss as a place to start re-negotiating.