[nixgeek]

Regardless, make sure that this person's documents and other personal files are backed up.

Once that's done, you could just perform an "Erase and Install" and that would wipe the drive clean and install OS X. However, you would also have to make sure that the person isn't attached to any apps that she might not be able to reinstall due to lack of discs or whatnot. If this is an issue, the better option would be to perform an "Archive and Install." This will basically replace the System folder that's on there now with a fresh one, while leaving her documents and applications intact. There should be a folder entitled "Previous System" or something of that nature after the "Archive and Install" installation is finished.

Personally, I would perform the "Archive and Install" option first and see if things get better from there on. If not, then take it to the next level.