Yes, I think you're right. That's what I get for not double checking. Samantha is credited for guitar and cello on all the albums (so far).
As Quadfather said, Requiem - Mezzo Forte is definitely their best release. I very much enjoy Requiem - Fortissimo and I always listen to it straight after it's predecessor, but it certainly isn't as grand and lacks in comparison - it is a great album in it's own right, however.
I can't wait for the first part of the trilogy, Requiem - Pianissimo to be released, so I can listen to the whole thing in one go - I anticipate that it's effect will be far greater this way.
But definitely look into aquiring Requeim - Mezzo Forte, even if not the other two. You won't regret it.