This reproduction method is certainly not something covered in the general Alien Reproduction method. I think it is some kind of mutation or failed attempt at evolution. Ya know, in the novel
Relic, one of the characters, Dr. Frock, talks about his theory about evolution and mass extinctions, what he calls the
Callisto Effect. This Callisto Effect proceeds like this more or less: at a certain point, in a determinate population of a species, appears an abomination, different from his regular kind, that with mating with normal individuals will create a new mutated generation that is no more than the next step of the Evolution of that species, and be the likely cause of competition with another.
The Predalien shown in AvPR could be one of those Abominations, and her "sons" the next stage of the Alien evolution, even if it doesn't really seem so.