Because Rosalie hates Bella but Jacob is Leah's friend and Jacob cares about Bella so if she died, Leah would be sad but probably only because of Jacob's pain.

Rosalie doesn't care about Bella so she wouldn't really bother to keep trying to bring Bella back. She'd just say, "She's dead, we can't try anymore."

I picked Rosalie because in "Breaking Dawn" It says Rosalie wouldn't care if Bella died because of the half&half baby, she would just take it from her. Or something like that.

Also because Rosalie is jealous of Bella in many ways. One she can get pregnant and have kids. She has a life. She hates her because Bella wants to become a vampire and throw away her life, she says. Rosalie wished she wasn't a vampire...

What do you mean by this exactly?

Well they both hate Bella a LOT. It was just a random question because Edward and Jake both loved Bella, and Rosalei cared about Edward and Leah cared about Jake. So they'd both be hurt by Edward and Jacob's pain if Bella died but who would be hurt longer was really the point.