Use GCFScape and open up the Portal 2 content file, found at \steamapps\common\portal 2\portal2\pak01_dir.vpk (for some reason it's unlike TF2 and HL2 which use .gcf's)
There will be a directory structure visible in the program, browse to \root\sound\vo\ and go nuts with probably close to 1000 audio files in a couple folders:
\root
\sound
\vo
\announcer
\cavejohnson
\core01
\core02
\core03
\glados
\turret_defective
\wheatley
Cores 1, 2, and 3 are the...
"space", "fact" and "adventure" spheres, respectively.
The final JoCo song is \root\sound\music\portal2_want_you_gone.wav,
...and some other talking stuff (turrets mostly) are in the \root\sound\npc\ folder.
Outside of the .vpk with the audio files, the subtitle file can be found at \steamapps\common\portal 2\portal2\resource\subtitles_english.txt (or _czech, _danish...) You can actually use this to quickly find an audio file by searching for a word or sentence fragment, e.g. "nine":
"announcer.openingcourtesy01" "<clr:250,231,181>Announcer: Good morning. You have been in suspension for nine nine nine... nine nine ni- This courtesy call is to inform you that all test subjects should immediately vacate [FADES OUT]"
The related audio file would be in the .vpk, \vo\announcer\openingcourtsey01.wav
GlaDOS is made up of a few different personalities (the personality spheres), and Caroline was probably one of the ones that was integrated closest to GlaDOS. It's fairly likely that Caroline's more closely integrated and influenced aspects of GlaDOS's development, but GlaDOS clearly has her own personality because otherwise she probably wouldn't have flooded the enrichment centre with a deadly neurotoxin.
There's a much simpler explanation for the turrets ignoring Chell; GlaDOS no longer wants to kill Chell, so the turrets no longer recognise her as a target. Because they're made by Aperture, though, they're quirky enough to recognise Chell as an audience instead. Hence the singing - you can run across them practising earlier in the game.
Best Answer
GLaDOS is refering to Caroline. Here's why I think so:
Caroline was a part of GLaDOS. Perhaps Caroline's personality was merged into the master system in a way similar to how they modified GLaDOS' personality by adding core modules to her (although not exactly the same way). Or perhaps GLaDOS started off as Caroline, but mutated or was modified into something more. Either way, the more menacing side of GLaDOS decides she no longer wants her more human "Caroline" side, and deletes her. She says goodbye to her in song as she does it.