It probably won't be a 2nd Christina song. I've never seen that done.

But they perform two songs usually. The first one is "stripped down" in that they come out rather "normally" dressed and sing the song. They're typically alone.

The second song is a bigger production number where they're usually wearing costumes, they bring out dancers and sometimes the original artist. (Although the original artist has made appearances in the first 'toned down' performance.)