I'm not sure I understand your thinking.
While it's apparently known that SN offered to drive her, she said no. His reasons for asking, and hers for declining, would seem fairly transparent and incredibly common at the end of a night of intoxicating substances. (He thinks she's possibly too tired or messed up to drive, she thinks she's fine and wants to get home WITH her car.) Any adult who has ever been in a bar with friends at closing time, has at some time been on one end or the other of that conversation, I bet.
Since SN accepted her choice without ado, by implication he accepted that she had the ability to walk to her car as well, prior to a drive. Perhaps he even figured the open air and exercise would do her good and increase her ability to be alert as she drove.
I don't see anything in that common scenario that would raise alarms somehow (for being out of the norm, that is).
Can't speak for Cookie, but when I responded to this same quote of EA being her ONLY choice, I was pointing out that NO, he wasn't her ONLY choice. MOO