Both
Chat with our AI personalities
Bella says this because Alice can see the future, so anything Alice predicts will most likely come true. Alice has seen in her visions that Bella will become a vampire. Edward doesn't want such a future for Bella. He's against it. And then Bella says - I'm betting on Alice. As in, 'I think she will be right'.
Because later that night Bella and Edward make love. Alice knows because it is their honey moon they will do this so she thinks it will be fun to put in ligerie for Bella.
well i don't want to be a huge spoiler but in breaking dawn edward, Bella, and Alice graduate
Because Rosalie told Edward that Alice told her that Alice saw Bella jump off a cliff and drown. But Alice couldn't see Jacob saving Bella, because by then he was already a werewolf. And Alice can't see any future to anyone if it involves a werewolf.
She doesn't want Edward to know that she is trying to save them. Alice left the note there for only Bella to see. If Edward knew that she was trying to save Renesmee, he would say it was too dangerous and wouldn't let her.