Morning sickness

Okay so me and my sister are pregnant at the same time (crazy right?) She's only a few weeks behind me though. I'm 12 1/2 weeks and she's 10 weeks. Only a few times, (very rarely) have I felt nauseous or had morning sickness, no food cravings and I'm not really picking up any weight where as my sister gets morning sickness and nausea almost every day, craving certain foods and is gaining weight quit quickly. I've read things that said that the more morning sickness you have, the more healthier the baby is going to be. Now is this just a theory or is it a well known fact? I've also read things that said that every single pregnacy is different and not every mother is going to go through the same things as the other. I first thought I was lucky to not have any nausea, MS craving or weight gaining but now I'm a little worried. Any thoughts???