To be fair, if they plan accordingly, she's a lot easier to deal with. Even pre-nerf Xanesha can probably be taken down fairly easily if you don't climb up the Tower, but go in from the top. Personally, I'd reward them for thinking tactically about things rather than just kicking in the door and taking their lumps. They should be rewarded for smart play, after all!
Yeah, my group considered flying to the top of the tower, instead of entering through the door and working their way up. They decided that would use too many of their spells, so they might not be ready for what they faced (it would have taken all of the sorcerer's 3rd level spells for the day). But it probably would have made the whole thing so much easier that her lack of level 3 spells wouldn't matter.
As is, the tower offered some minor challenge until they got to Xanesha, which was a tough enough fight to scare the heck out of them. I could have killed a PC, but I had Xanesha attack the most immediate threats to her instead, which was a mistake on my part. She should have targeted the healer first (after seeing him heal someone), even though he wasn't the one hurting her. So there should have been a PC death, but I messed it up, and they just barely escaped with no deaths, despite 2 of them hitting -10 HP at least once during the fight.
And the petrification mask was a bust. That DC 15 (IIRC?) save is just too easy at that level, especially since I had her try it on the healer, who she had no way of knowing would have a better fort save than most of the others.