Or maybe unused dialog that's stored in the BSAs.
http://www.audacityteam.org
audacity is very easy to use (and free), you can splice any audio files together you want, use filters to change the pitch, cadence, background. There's filters to smooth transitions, its pretty fun, i've used it on my other mods for custom sound fx, i downloaded a bunch of public domain audio samples and made some pretty cool stuff.
eventually i'll probably use it for FO4, since the MC is voiced.
you need more than audacity, that's just for editing the actual audio files. You can follow these tutorials to get you started,
https://forums.nexusmods.com/index.php?/topic/577443-tutorial-adding-custom-voice-even-if-the-ck-wont/
http://deck16.net/post/22645519500/making-a-unique-voiced-follower-in-skyrim-part-1
You should be able to add any type of custom audio files, even overwrite NPC voice files.
Cut 'n' splice existing sound files. Extract from archive, extract wave file from fuze, edit, re-fuze, re-archive. I've done it myself. Over 300 lines. Its unbelievably tedious but possible. Your limit is the amount of dialogue recorded, there more there is of it the more you can do with it.
It'd be fine for your own use but you can't release it publically.
You should be able to get away with releasing a mod that uses Morrowind or Oblivion assets, as long as you require them to own both games. edit: and by this i mean, you couldn't release any assets publicly, you'd have to have a program that looks for the file in the default folder of whatever game you're trying to use assets for.
modifying assets requires it be something like 30% different than the original for fair use. The problems you would face wouldn't come from Bethesda, although that wouldn't be off the table, it would probably come from sites like the nexus. splicing audio from morrowind might be technically legal, but its a thin line that probably won't fly unless you have written permission from bethesda to do so.
I would just try to get a voice actor that can mimick her voice and then match up the inflections and pitch in audacity if you wanted to get crazy with it.