yes, I went for the charity concert in July last year, she was
one of the singers. Really, she doesn't have the stamina to sing
more songs compared to other singers!! For the charity concert, the
one with the stamina and sang the best is Jeff Chang. Can't help
but when I heard him sing "live" I was very touched and tears
rolled down my cheek. He has very powerful voice, soothing,
wonderful, great singing!! 
Harlem Yu not too bad, but his singing is kind of like
shouting, oops sorry I don't mean any harm but this is what I find!
As for Jolin, she is a disappointment where "live" singing is
concerned, though she danced quite well. Think better to see Jolin
dances than sings - she has no stamina in singing! 