If you're saying that just based on tonight, are you sure you didn't just hear Frankie drowning her out? She really isn't bad at all. It's hard to find live HQ solo performances of her since I don't think she has promoted any solo releases but you can hear her quite clearly over the backtrack in that link and she sounds better than a lot of current artists (*cough*Rihanna*wheeze*) and manages to dance a little still.

ETA: Switched the link to a performance that only has backing vocals for the chorus.