I'm finding a lot of good deals on the non-overclockable i7-2600. (Note, no K!)
If you're looking to max out on the cheap, that's the sure-fire way to go. The 3770 next generation is nicer but not guaranteed to work unless a BIOS update adds support in there, plus I've been finding it 50% more expensive!
It's selling cheap because it's older - but still awesome! Best $120 you could spend if you actually need the CPU power at all. If she's not needing that power, some extra RAM and a larger+slower SSD would likely make her machine feel more 'peppy' than the i7 would.