I think it's the obvious one because SP is alive. Sure, abductor #2 might have been otherwise engaged, but it seems logical that with one person driving, it would be ideal to have a partner to control SP and get her out of the vehicle as quickly as possible.
Anyway, Lake16 seems to think it's an important detail, so I do too. I was hoping to elicit other theories, is all.
Could it be that abductor #2 holds some kind of a job that she would have to be at work at that time on Thanksgiving Day? I'm just trying to think outside the box.