Her grandfather did just get killed in front of her. Some people would prefer to grieve without being around other people. What she owes them isn't gonna go away any time soon, but neither is a nagging little voice in the back of her head asking why they couldn't get there just a little bit faster. She needs some time to cool off away from them, I'd say. Particularly since she also just got powers, so there's another little voice for that one, why didn't I get this faster? She's got shit to process.