I think it's supposed to be something to do with the fact that Yoda knew Darth Sidious was going to hunt down all the Jedi and exterminate them, and he and Obi-Wan knew that Luke and Leia would be there only hope, so they had to keep a low profile. I think this is supposed to be a mixture of impressions of her real mother, Amidala, through the force, in later books we see women who are pregnant with force sensitive kids getting strong impressions from them, even when in the womb. It may also be that Leia is confused with her adoptive mother, who we know has has several miscarriages, which i imagine would leave her pretty unhappy from time to time. I think that's a genetics vs environment thing. Having read the Clone Commandos books it shows how the clones develop very different personalities from each other, all the same physioplogically, but distinctly different at the same time.