I've done a bit of research with this as well

It seems to go along with the usual pack order. Dogs like to appeal to the alpha. So, whomever they view as the alpha they try to appeal towards. They also like to be the alphas favourite and view whomever gets the most attention, etc, as the alphas favourite. This is what I've read and also, for a tiny part, experienced. Spanky (little Chi girl) does get irritated if my husband pays attention to one of her kitty siblings. However, it's probably the mildest case I've seen of this behaviour and she's stopping it, slowly.

A solution I read about would basically go like this: Puppy is in your lap, another person approaches. Puppy becomes agitated. Discourage behaviour from approacher, discourage agitation from pup while reassuring her.

I haven't tried that solution so I don't know if it will work.