That reason is snuggled up between Anissa and Mariella:

That's precious baby Antonia, and we all fell in love with her during our much-too-brief visit to Toronto over American Thanksgiving. It was fabulous as always hanging out with Natasha, Mariella, and Dan (and his brother Jonas), but that little sweetheart stole the show. So I can't really blame Anissa for wanting a baby sister, too, just like her (still) best buddy Mariella. As she explained this weekend, baby girls are just fancier than baby boys!
I have no feeling either way if it's a girl or a boy doing gymnastics in my belly every night when I'm trying (unsuccessfully) to sleep, but I suspect that when this little munchkin makes his/her arrival, Anissa will be tickled pink no matter the gender.