Could someone help me reasoning about Brook's vote to eliminate ***

If she didn't, it's a 4:4. She's safe, given the necklace. Simon is safe, then 2 of their team are unsafe, while 3 of the other team are unsafe. It's better odds for them. She can easily cruise to the top 6 before eliminating Simon.

Now, with the other challenge beast gone, she will be out once she loses.