It is quite normal for queens to be territorial during their pregnany, and sometimes even more so when they have kittens. Usually it will go away after, but some cats just don't like other kitties from the start
It usually gets to its worst after the kittens are born. They may lash out at any other cats who come nearby and they should always be given privacy from any other cats for the first few weeks after they give birth. Otherwise they could be worried into abandoning the kittens.