Sumner B Period discussion

In chapter 3, Motives, Bella and Edward are on their way back from visiting Bella's, mother Renée, in Florida. Edward, on the plane, asks Bella if she is sad to leave her mother knowing that she might not ever see her again, or at least not too many more times, once she becomes a vampire. Bella responds on page 65 when she confesses that she is, "More relieved than sad." This statement made me kind of confused about Bella's relations hip with her mother. I know she loves her mother very much, but they seem like their roles are reversed which still does not make sense that Bella would not be more upset about loosing her. It is crazy to me that she wants a relationship with Edward more than with her mother, yet she is hesitant to marry Edward. I know Bella was scared that her mother was beginning to see that there was something weird about Edward, but the fact that she says she is relieved to not be with her anymore astounds me. Bella is ready to give up everybody and everything she has ever known to become a vampire forever, but she she is scared to be with Edward forever.