I love your answer and share your opinion. But that's also why The Ring 2 wasn't really good because they made it official: Samara has been adopted. But, if we forget the second and third movies, there is an obvious hint that the Morgans require some sort of evil forces to get a child because Anna couldn't be naturally pregnant. Also, it could be a start of an explanation about why Samara is evil and why she got supernatural abilities.
Answer: She's infertile. She wasn't ever supposed to have children. It's hinted that she made a deal with evil forces to have Samara.
Grumpy Scot
I love your answer and share your opinion. But that's also why The Ring 2 wasn't really good because they made it official: Samara has been adopted. But, if we forget the second and third movies, there is an obvious hint that the Morgans require some sort of evil forces to get a child because Anna couldn't be naturally pregnant. Also, it could be a start of an explanation about why Samara is evil and why she got supernatural abilities.