How do you keep your parents from hacking your computer?

[Sir Nerdsy]

Change your password, first, to something that you can remember, but is hard to guess...

Then, change your email password, with the same parameters.

Set your browser to delete cookies upon closing, or to never accept them from sites (Doing this will require you to log-in to all sites every time you visit, and if she does not know your password, whala)

If you don't know how to do this, specify what browser you are using, and I will edit my answer tomorrow morning.