Honestly, not surprised that she is only doing 6. That said, this sounds very oddly like what Lloyd Webber did in the original Evita with Elaine Page. Susannah Fellowes wasn't on a set alternate schedule, it just said "at certain performances" so you might show up 4 times in one week and get Fellowes, and you might go all 8 and see Page. There was no rhyme or reason, and you had no way of knowing who you would get going in.
If RIpley is only doing 6, then there needs to be some sort of caveat on the playbills and promotional materials saying so.
They also need to sit her down and say "OK, you can skip either matinees, or one matinee and one evening, but NOT the weekend shows."
Tony Award or not, this is incredibly unprofessional, and I've lost a TON of my respect for her.
http://www.youtube.com/huskcharmer