Rachel has the unlikely combination of athletic ability and experience and a high starting weight. This is pretty common in the men, who are often former athletes, but has been less common in the women. The Wikipedia page for this season shows that Rachel has already lost 99 pounds. That means she has lost 38% of her starting weight in 11 weeks. Here is some data from the wiki with the contestants sorted by their percentage lost:
|Name||Age||Height||Starting BMI||Current BMI||Start Weight||Most Recent||Percentage Lost|
This makes it even clearer that Tanya, not Tumi, would have been the one to go home if this was strictly a weight-loss competition and not a reality TV show.
Because there is a triathlon coming up where the winner will be guaranteed a spot in the finals, Rachel should make the finals if she can compete in the triathlon. She is a former champion swimmer, and she's also one of the best runners on the show. All the contestants do Spinning. She just has to make it to the last challenge before the finale:
For the first time in series history, licensee partner “The Biggest Loser RunWalk” will host an in-show Mud Run and first-ever triathlon where each contestant swims a 1/2 mile, bikes 12 miles and runs over three miles as the last challenge before the live finale.The swim is long enough that someone who can swim well is going to have a big advantage. Contestants might be able to fake it for a few hundred yards, but not for half a mile. Rachel's only issue is making it to that triathlon -- if she ever has a bad week, she will definitely be eliminated, just like Tumi.
The moral of the story: If you ever decide to try out for The Biggest Loser, learn to swim first!