This is by far our most memorable and challenging encounter, and we could not have survived it without action points. Having turned Ironbriar and his murderers over to the authorities, we decided to go after Xanesha immediately so that news of Ironbriar's defeat did not reach her ears. Thus, bruised and battered, we found ourselves on top of the roof about an hour before dawn. We were six 6th-level characters.
The first PC to "see" her was Sandoz, our warlock, who also saw through her illusion. She turned him to stone while floating calmly out of reach.
I unravelled many of her spells with dispel magic, but she just laughed and started buffing herself again.
Our monk took a flying leap through the air to try and grapple her (no, he could not fly and did not have feather fall, so we're not really sure why he did this), but she critically hit him with her AoO. Our scout had to catch him and pull him back onto the roof so that our cleric could heal him. Our fighter unlimbered his heavy crossbow.
As the scout and the cleric healed the monk, I used a scroll to cast fly on the fighter. Xanesha then shut us all down with silence.
As the fighter went toe-to-toe with her, we toppled the angel on her, shot arrows at her, and ran around trying to find a place where we could cast spells. She then dismissed the silence to taunt us.
That was when the warlock recovered and hit her with his eldritch blast (go touch attack!). This really turned the tide, as we struggled to keep both the fighter and the warlock alive. According to the DM, she would have escaped via dimension door after the fighter buried his axe in her (critical hit) had the warlock not blasted her twice with his last action point. It was an awesome fight, though we went way past when we normally end sessions.