Help me make my first BBEG!

[Neronoxx]

Hello everyone, this is my first time posting here. My friends and I are starting a pathfinder campaign, with me as GM. I'm a sucker for narrative, so the campaign is going to be set in a dark fantasy setting. The idea i have been playing around with is that the PC's are invited to the capital city of a kingdom, where they discover that there is a serial killer on the loose. They are asked to investigate and find the killer.
The killer turns out to be the princess, who with the help and urging of a demonic text, believes the royal court to be conspiring against her sickly mother(who has actually contracted a disease that is slowly turning her into a zombie.)
Here is the catch; The Princess is an X level wizard who uses phantom killer to do her dirty work. She is never at the murder scene when it happens, instead casting the spell from a distance, out of sight. With her status protecting her, and her docile nature, she seems like the last suspect on the PC's list. Basically, i need help leveling her up to a reasonable threat level.
The ordeal is more of catching the princess, rather than the actual fight. She isn't going to be able to actually fight the PC's rather well, so escape is her best option. She can even use her status as a weapon against them. Even when they catch her, the PC's judgment on her punishment would send shock waves through the kingdom. She would rather run than fight, so i have given her a bunch of spells pertaining to that idea, but what do you think? Any spells or items a must have? She is a princess, so the acquisition of rare items is not a problem.

[I3igAl]

Well "Contingency: Teleport" is all you need to get away from any situation. She'd need to be a wizard 11 to konw both. If your players aren't high enough to have such a highlevel villain, just have her cast it from a scroll.

[Democratus]

Since she is clearly loosing her sanity it leaves many options open.

One dramatic way for her to "escape" is for her to kill herself if cornered by the party. She has an assistant who has been keeping a Clone (as per the spell) ready to revive should she perish.

Now the party can be framed for killing the princess while she safely plots her next move in anonymity.

The 'assistant' could actually be a cleric of a god of madness and suffering. Through the princess, the cleric could bring about fear and suffering to a whole kingdom - thus spreading the good works of this god.

As for spells for an increasingly insane serial killer, subterfuge is key: Disguise Self, Memory Lapse, Obscuring Mist, Nondetection, Suggestion, etc.

Good luck with the adventure. Sounds like fun!