Katherine Jackson At Arizona Spa

Katherine Jackson is at a fancy spa in Tucson, Arizona, but the big question now ... why did leave Michael Jackson's 3 kids?

Sources tell us ... Michael Jackson's siblings took Katherine from the family compound in Encino, CA to the Arizona spa, because they feel "the house is utter chaos" and Katherine is exhausted.

Here's the mystery ... Paris and presumably the other 2 kids were never told Katherine was leaving and it's been a week since they've seen her. So why would Michael's brothers and sisters yank Katherine from the home when she is the only parental link to the 3 kids who are still coping with their father's death?

Sources familiar with the situation tell us ... there's a "concerted effort" to get Katherine on board to challenge Michael Jackson's will and get the Executors removed. In addition to Randy and Jermaine, Rebbie and Janet are also on board, although it's unclear exactly how much Jackie supports the move.