It does run faster/better with CM6.1 than with stock. It definitely made her happier with the phone. Angry Birds became usable for her! :-) It also freed up a lot of space for apps.
Voicemail got slightly weird; she gets text messages for each voicemail left.
The phone is still slow and a little flaky though, and she's anxiously awaiting the day when she can get a new phone at a reasonable price.