The plot of "The Ring 2" is pretty simple: After Rachel discovers that people are still copying the cursed tape (a trend she started, it's worth noting), she attempts to burn the first new tape she finds. This only incurs Samara's wrath, and Samara goes after Rachel by slowly possessing her son Aidan.
"The Ring 2" is primarily about childhood trauma. At the end of the first film, Aidan sees his father die and only escapes by helping his mother transfer the curse onto others. Rachel is an adult, so she tries her best to compartmentalize what's happened by rationalizing that she had no other choice than to save her child.
Aidan, however, is a child who doesn't have the adult tools to cope with what's happened to him. He is both literally and figuratively haunted by Samara. When he becomes possessed, Aidan becomes so cold that it reads as a physical illness. And in the real world, it's not uncommon for emotional trauma to lead to or exacerbate physical illness. In "The Ring 2," doctors at the hospital suspect Rachel is abusing Aidan because none of them are able to diagnose what's really happening to him.
The story is also about how adults need to deal with their trauma, too. In a way, you could argue there's a kind of abuse happening between Rachel and Aidan because Rachel is ignoring her family's trauma, which is having aggressively negative effects.
