The thing is, from Vicki's perspective, she can't actually stop Laura, unless they start playing endless, ridiculous games, where Vicki keeps standing in Laura's way, and Laura tries to push past her this way, then another... then a scuffle ensues, etc.. [spoiler]She's actually more right than she knows. Even that wouldn't help.[/spoiler] That's what's unfair about Liz's order. Vicki's not a bouncer. Maybe she's used to Matthew being there for that...
Laura asks Vicki why she's "enforcing" Liz's ban on her, and V says "It's my job." If so, then it only became part of her job a few minutes earlier during her talk with Liz; it never was before, and she's not going to be very good at it.