Alternatively, you could ignore the more involved and long term plans for settling this girl's hash. Remember, she expects you to try for a long series of solo games where you attempt to become more powerful than she could possibly imagine. She will then try to continually outwit you, and given events so far, will most likely succeed.
Play a VERY short series of solo games, with a single GM that you can trust to keep EVERYTHING you do a complete secret, even from his own characters, until it is far to late. The player who had the nun may fit the bill. Your goal is not to become a cybernetic monstrosity or an eldritch power, but to simply prepare a single event in the future. Hell, never replace your arm, just see to your wounds in the contemporary fashion.
The plan is as follows. After you make a basic recovery, find some event, or location, where the traitorous, usurping wench MUST be. At the appropriate time, see to it that said location is rigged with a very large quantity of explosives. More is better. Shrapnel, and anything else you can think of to prevent troublesome survivors would also be a good thing. Bonus points if you can get the entire party with her as well.
After setting things up with your specially chosen GM, stop attending sessions, until such time as the appointed hour draws near. When the time approaches, simply sit quietly in the room with your fellow players, smiling quietly. Then, when the clock strikes, let your smile grow to beatific proportions, and gently say "Boom."
After the presiding GM explains how the bulk of the party just got annihilated by outrageous amounts of explosives, explain how much fun you have had with your fellow players, and ask if they would be interested in starting a new campaign soon. After all, almost everyone needs to roll up new characters, and I'm sure someone can think of a plot hook set about 10 minutes after the explosion.