I talked to the ebookstore people and they de-authorized the Emily's home computer and left computer 4 authorized. So it got taken care of, finally! Everyone I talked to kept telling me to de-auth computer 4, but if I did that as soon as I signed back into my account to buy a book it would re-auth, lol. As long as I can read all the books I bought I don't care what they do! Thank you soooo much everyone, I get super confused sometimes.
(by the way I looooove my 600!!)