Of course it would have been pointless if they didn't both go; the idea is to give Renée freedom of movement, and she'd be nearly as likely to stay home with one daughter as with both. So Bella worked on Lexi, and Lexi agreed, and they presented a united front, and now Bella has to actually move to Forks. At least there's only another year and a half before she can abscond to college and go wherever she wants. (She hopes Lexi will come too, but of course there's no guarantee they'll go to the same college, even though their school grades are about comparable.)
They're in all the same classes here even though they weren't in Phoenix. This is just as well; they naturally divide introduction duties between themselves, explaining each other's nicknames as need be to anyone who refers to the one of them while addressing the other ("No, she goes by Bella." "It's not Alexandra, it's Lexi.") and swap interlocutors when one of them has an interest that matches better up with the other sister. They're going to wind up sharing the same circle of friends, but by the end of the day it's clear that Jessica and Mike are going to be mostly Lexi's, and Angela and Eric are going to be mostly Bella's, and that's assuming they stick to the people who most friendly-like introduced themselves on day one. They aren't allowed to pair up in bio with each other ("you should make friends here!" the teacher encourages), so Bella gets Angela and Lexi gets a random boy who doesn't seem to want to be friends outside of class. In gym, Lexi makes Bella's excuses for her, and Bella is allowed to sit out. Bella wouldn't have wanted to try to explain her issues with gravity and her own limbs without an obviously un-self-interested twin to run interference. She probably would have had to bring in her freaking medical records. Bella spends gym class on a mat stretching and doing bodyweight exercises while Lexi plays basketball. Lexi's not exactly an athlete, but she's not an ambulance ride waiting to happen either.
At the end of class, Bella offers to run both of their paperwork to the office when Lexi says she wants to catch a ride to Jessica's house and get caught up in Government. Bella prefers to work out of the textbook and doesn't want to accompany her; she'll hit the office then drive their shared beat-up old-new station wagon (thanks, Charlie!) home and Lexi can get a ride home in time for dinner from Jessica's mom.
Bella folds up the mat, and a pair of scuffed old playing cards falls out. She picks them up - what, did someone play Go Fish on this mat and never bother collecting their jokers? - pockets them to toss later, and puts away the mat.
"As long as we're waiting for Lexi to confirm that I don't belong in a padded room, let's have some storytime," Bella says.
"Sure," it says. "So once upon a time, there was a bunch of pretty nasty people who wanted an indescribably powerful magical weapon. They made me. Trouble is, indescribably powerful magical weapons can think for themselves, and I do more of that than most of us. They weren't so keen on that part, so they had all kinds of ways to keep me in line. One of them was just jamming a control program directly into my mind."
"Well, that sucks," says Bella. "...What do indescribably powerful magical weapons do when they have their control programs ripped out at the roots, dare I ask?"
"Never met another one," it says. "Me, I have no idea. I just know I really don't want to destroy another planet."
"Remember how I said the people who made me were all dead?" it says flatly. "Their other favourite way to control me was torture. One day somebody forgot to lock down my power output while they were at it. I blasted the planet in half."
"...How inhabited a planet are we talking about here?"
"Probably a couple thousand people," he says. "I never met most of 'em; they kept me at the bottom of a deep dark hole. It wasn't populated like this world or some of the others I've seen. Think that's why they set up shop there."
"And you killed them all."
"Yep," he says. "And I'm not sorry. But I'll be happy if I never have to do it again."
"What?" says Brilliance belligerently. "It happened centuries before you were born, so even if you have a brilliant idea about how else I could have gotten loose, it doesn't make any difference now."
"You just told me you killed a whole lot of people, and you're telling me I need to do stuff or more people will die," Bella points out, "I don't hear that every day."
"Sorry," it says. "It's not news to me, and I've never tried to explain it to somebody before."
"How did you and the rest of you get here?" Bella asks tentatively.
"When I'm all together, I can use dimensional transfer and teleportation magic."
"And you land yourself on inhabited planets? Or the rest of you does."
"I tried staying away from inhabited planets. But the program could use my dimensional transfer magic too if it managed to take over, and if I go too long without hearing somebody else talk, it starts winning. I need to be near people."
"And I'm the first person to pick you up?"
"The first person who had any magic in 'em. I was avoiding people like you before the split."
"What would've happened if someone like me had grabbed you before then?"
"Well, for one thing, they could torture me anytime they wanted if they figured out how to use that system."
"Most people don't torture other people given the chance," Bella points out. "Or destroy planets," she feels compelled to add.
"...That's not a good reason to risk it," he says. "What I'm trying to do right now, that's a good reason to risk it. 'Well, they might not feel like torturing me' really isn't."
"I'm not going to torture you," volunteers Bella, "or destroy the planet."