I don't think Pamela sounds very responsible. (Hardly a shocking opinion, I realize.) The way she reacted when Cynthia tried to correct her about things, for example--it seemed very juvenile, like she was angry that her pride was stung, rather than making her stop and think about how she should treat the baby differently. The way she sarcastically "apologized" for the seasoned salt shaker part is another example--IIRC, that was the only incident where one of the baby's parents (DH) actually told her to stop doing it; and later, at the end of the evening, that's the thing she chooses to comment on, that she has apparently been thinking about for a while, her tone and words implying that she is in no way at fault, and that the OP is overprotective.
I think one can come up with a lot of reasons why she chose to act the way she did with the baby (different standards than the OP, etc.). But to me the point is that when her opinions were challenged, whether by Cynthia or one of the baby's parents, she seemed to become angry and defensive, instead of considering that they might have a point or at the very least, that she should be following the standards of the baby's parents even if she doesn't agree with them. I don't want to project too much and come up with dire speculations of doom, but it's possible someone with this kind of attitude might think they know better than the parents and in the future let the baby/child do things that the parents have specifically forbidden--not believing the parents about allergies, for example.
So, I wouldn't let Pamela hold the baby again, at least not for a long time. It can be framed as "safety trumps etiquette," or it can be framed as, the OP isn't going to be able to relax and enjoy the party if she feels like she always has to keep Pamela and the baby in view.
I wonder if the OP would be able to talk to some of the other club members, like Cynthia, to see what their opinion is? At the very least it might be good to have extra eyes available to swoop in and take the baby away from Pamela, if someone else unknowingly hands him over to her.