Is verbal binding?
I generally agree with Dustin, but have to point out that this is very much a “you had to be there” scenario.
From your description, Brock, Anna didn't even put the physical card “on the stack” (i.e., she didn't even show the card, much less move it from her hand to the table or something similar)? and she stopped herself immediately, before Nora could react - thus, before Anna could gain info from a reaction.
I would do a quick investigation, to confirm what Dustin and I are assuming from your description, and then rule accordingly.
d:^D