May I offer a correction or two?
The author claims to be subject to this treatment (ie. what many would call "good customer service") because she's Black. You're correct when you state the white woman had no reason to assume the Black woman was going to sneak away without paying....
And, for all we know, she didn't. We don't know what she was thinking, do we?
A person of color wouldn't get in her space? Perhaps not. Ever shop at the Brooklyn Target? With a few notable exceptions the overwhelming majority of Target employees, who are persons of color, won't get in your, or anyone else's space. Even when you need them. They're usually too busy chatting, texting, or just hanging out.
This is especially true of Atlantic Avenue store. The cause of which, I believe, is that many Hasidic Jews shop there, & it's likely that the employees have come to assume that most of the white shoppers are Jewish, & thus unworthy of their assistance or consideration.
It's not narcissism to to have an issue with being treated this way ... but it might be paranoia. All the author actually described was good, proactive customer service. Did she consider that perhaps the woman was being evaluated? That her supervisor was watching & she needed to follow company policy?
Note, earlier she wrote of preferring to use self-check out to avoid having her purchases judged. I feel the same way. But I also know that in a busy store like Wegman's cashiers have no time to ponder each item on the conveyer belt.