My 'gut' feeling about Mary EVA is that she was born in Cornwall to Thomas EVA. There are a couple of births of a Mary Jane around 1856/1858 and the 1861 & 1871 do show a couple of Mary Eva's with Thomas.
I'd guess that her birth place shown as Cardiff is not correct and I suspect that Mary believed that she was born there. The Registrar's office in Cardiff have searched their registers and cannot find any details of such births in the Cardiff area.