On a microo-hop such as DCA-ALB in a small aircraft, it is entirely possible that turbulence shortens the time available for service and thus the beverage service is cut short, especially with only one FA.
I presume that the FA's comment about the other carts is that she was directed not to unlock them (not really a lock, but a knob) so that they couldn't go wandering.
Generally speaking, I've never been denied my choice on mainline or express other than when turbulence interferes.