FlowerPower, I totally agree that clip of Ali is from the Episode 1 Immunity Challenge. Here is a clip just a little later where you can see her top and sawdust in her hair which matches the preview of the Ep1 Immunity ChallengeShe definitely appears to be celebrating. However there is this commercial of a future challenge showing Ali and the rest of the Hustlers except Lauren. Ali's top is different than the clip above so definitely not from this challenge. If this is Ep2 challenge and Lauren is not there then Hustlers would have lost Ep1 Challenge or maybe this is Ep3 challenge?
Here are some other possible future challenge shots from the Preview...
Ashley possibly in a swimming challenge?
Dr. Mike in challenge with country signs
Desi possibly in a swimming challenge?
Ali possibly in a swimming challenge?