Why did Kim take Crystal to Kroger's in the first place? I know the guard was a female. Did Kim know the guard? I think so.
I've never figured out why Kim took her there. I think you're right, she might know the guard or at least know someone who worked there.
She needed to take her someplace safe. Otherwise she might get implicated in something. Krogers was probably closer than the local Walmart or all-night grocery store.
The Kroger guard was a black female.