Board Thread:Naruto Discussions/@comment-28861328-20140618060932/@comment-3568954-20140618083025

Kaguya ate the fruit which gave her the power of the shinju the shinju was made of nothing but natural energy when it hit her body she was capable of molding her Physical energies with her spiritual energy(chakra is made of spiritual and physical energy) as such the shinju's power allowed her to combine said spiritual and physical energies creating chakra it never said that originally kaguya and the shinju were one entity but that they became one entity when she ate the fruit also they showed it. the juubi is the aggregate of all the tailed beasts chakra(which is really kaguya's chakra) the body of the juubi is the gadou mazou so essentially kaguya's original body is the gadou mazou she likely mutated her body into that form and changed into the juubi.