Does anyone know what happened to Mary McCarthy, daughter of Hugh & his first wife Rose?

Mary was bapt 4 Aug 1839, at Castletown, IOM.

A Mary McCarthy emigrated to Victoria, Australia in the 1850's and married or lived with William John Shannon. They had about 10 children.

Tradition has it that Mary came from the Isle of Man and her father was a gardener. I'm wondering if she could be Hugh's daughter - he was originally a gardener before taking over as inn keeper at the Manx Arms. Mary's first son was named William John after her husband and her second was called Hugh James, which would probably be the name of her father.

I'd be very grateful for any help on this, even if it's to be told that Mary McCarthy from Castletown died in infancy!