According to the message-board blog on Aruba.com, which has a string of comments on the Natalee Holloway disappearance, Beth Holloway Twitty has a maiden name of Reynolds and hails from Arkansas, originally.
Paula Hitler had no children. Angela Hitler had a daughter named Geli who committed suicide.
Alois Hitler, Jr. had a son by an Irish woman, and he was named William Patrick Hitler. He migrated to the U.S. in the late 1930s and eventually had four sons. One is now deceased.
Two of the three sons had no children ( according to Wikipedia ).
William Patrick Hitler changed his name after serving in the U.S. Navy in World War II. He became William P. Stuart-Houston.
It is difficult to see how Beth Reynolds could have a direct link to the family of Adolf Hitler, as neither his sister nor his half-sister fit the criteria.
Perhaps more digging will turn up something but it looks very tangential and non-related now.
A news editor in Alabama said that he believes that any comment by Natalee linking her own mother and Hitler refers to the fact that she considered Beth to be a very 'controlling' individual and that it may have been only a not-very-humorous reference.
I.e., she may have said, in jest, that her own mother was "a little Hitler" or a little like Hitler, or "just like Hitler."
It would seem to be a very big stretch to go from such a typically rebellious and off-hand comment to a real consideration of being a blood relative ( however far removed ), to any of the children of Alois Hitler ( probable origin of name, Haidler or Hittler, once meaning "shepherd" or "herdsman" ), or Alois Hitler, Jr., his son.