Roundabout
It's the anger in her eyes that tells you how right you are. She's so angry - angry that you had to go through what she's fought so hard to get past, angry that the world isn't as perfect as she thinks you deserve it to be, angry that you can look at her now and see something she's kept hidden for years. There's been anger there since the two of you peeled out of the Silver Bullet's parking lot, your face bloody and your dress ripped and her hair not behaving itself for the first time since you've known her.
At first you didn't understand the anger, not quite. Was she angry with you? She shouldn't be. It was your first time out of town without Darryl constantly on your case, and you'd only wanted to have some fun. It wasn't your fault... you'd just been dancing, and then suddenly you were bleeding onto the trunk of a parked car with your dress around your waist. And then Louise was there with the gun you'd never wanted to know how to use, and then Harlan was dead and you were running.
She wants to get to Mexico from Oklahoma City without going through Texas, and she's angry again that you're asking her why. It's a crazy idea, even if it would be bad to get caught in Texas for blowing a guy's head off when his pants were around his ankles. But she's not only angry, she's hurt and withdrawn and overcompensating, and you've known her since you were both too young for anyone to even think about touching you that way - except apparently she wasn't.
She moved to your town in junior year, and it hurts to remember, because now you understand why she was so hard to talk to, and why she didn't want a date for homecoming. But even though you were a popular cheerleader, you talked to the girl who always wore her hair in a bun and hid behind big round glasses, and the two of you got to be friends. Even though she didn't talk to you for three months after Darryl got to third base, she was around when you were crying over rumours that he was seeing another girl, and you love her for that. You love her, too, for the strength she's always had when you needed it.
So you're going around Texas to get to Mexico so that she can pretend that she's as strong as ever, that everything she's done has been for you, that's she's not even closer to breaking than you are. She's always protected you, from the catfights at prom as much as from Darryl's asshole behaviour, and now you know that it was because once, she couldn't protect herself. You're sure she thinks that she's failed again, that even though she saved you from Harlan, she's doomed you by running like this, and so you look at the map and pretend that you don't know.