My wife tried to to start her 2004 cavalier with the wrong key, and now the ignition will not turn with the right key

Hello foxrider.
Chances are when the wrong key was put in it may have damaged the lock tumblers.
The lock cylinders on these cars are enough of a problem using proper keys.Not very well made to begin with.
You could try a very light oil such as WD40 to lubricate the tumblers in case 1 may be stuck up into the barrel of the cylinder and gently run the key in and out several times.
Jiggling the key inside the cylinder will sometimes loosen them up too.
If you do get it working it may be a good idea to replace the cylider and key soon as it may fail you again.
I hope you succeed in getting it to turn, otherwise it may be a job for a locksmith.
Good luck with it.

KL

If its just the key tumbler not turning you may have stuck a pin inside the tumbler into a jammed position with the wrong key. Now the right key wont bring that tumbler pin back down.

A little lock oil on the right key run in and out with a little light tapping on the ignition key body might free a stuck pin up. Get the lock oil they use on frozen locks just to be safe!

I hope helps. Good luck and be careful.