Latest media reports seem to be leaning towards the aircraft having encountered larger than expected waves, skidding onto the beach and colliding with vegetation. Seems to suggest the expected deceleration after touch down with the aircraft coming down off the step didn't occur and the aircraft's continued onto the shore with some speed. There's been no further mention of the plane having flipped over.
Woman injured in Whitsundays seaplane crash - ABC News (Australian Broadcasting Corporation)