Is this offensive?

I would have a nice pic, but my computer/cell phone suck.  I emceed the Funny Bone’s open mike Tuesday night.  Before the show a middle aged black woman showed up…with black face…wearing a kerchief skirt, head scarf, and high socks.  As the hilarious Darrell Dawson said onstage, she looked like the housekeeper lady on Tom and Jerry (sans broom).  She read nursery rhymes and talked very stereotypically of a character written by white people in the 30’s.  A lot of “I’is” and “yous’s” and what not.  Upon returning to the mike, I said, “That reminds me of my nursery rhyme: Hickory Dickory Dock, is it offensive that a black woman has blackface?”  I don’t know if her actions were offensive, b/c she was black.  I heard a black man say it was b/s.  A black woman said it was acceptable.  Discuss!  I only know if I did it, definitely offensive.  Either way, it was terribly unfunny and I hope she never shows up again…