I think that Christine only has the one Yamaha 7' grand from Songbird & touring homage.
In her house, that is. Her studio/barn may be another story.
I actually wonder if she's kept her portablized B3. It is not shown in the videos on her website, but her Yamaha KX-88 controller is. Of course, we still have no idea what she's using for patches, as the KX-88 is just that, a controller with no onboard sounds.
Now, as for rating pianos.. I've played many types. They are very different, though all pianos are different.
Steinway is your all around piano. It embodies what most pianos are. I've played a Bosendorfer once, for a concert this past spring. It had a dark rich tone that was very pleasing and interesting. And let me tell you, there isn't much use for the extra keys at the bottom. I tried to throw them in on something, but it was jazz and and the music we were playing wouldn't get much use of them.
Yamahas tend to have a brighter sound, which makes them more ideal for playing onstage.
Kawai pianos (especially uprights) are utter crap. We have a contract at my college and get a dozen new ones every two years. The new ones came this semester and they're just as bad as the ones from last year, except they haven't broken down yet. We have two Kawai grands-a 7' and a baby grand. They are decent, but not superb. Unfortunately, our 9' Steinway rarely gets taken out.
So yes, I can understand why she might like them, but then again, she's been using their products for years, so it makes sense.