Ive seen the castlist for the 1st of may on the website and june whitfield is potraying a nun and it reads that kat has gone to revist where she gave birth. Could this all tie in with their move to ireland? I think it would be a brilliant story

Historically she didn't. It was established in 2001 that she was born in a hospital, and subsequently mentioned again in both 2005 and 2010.

Don't be shocked if they try a retcon on it, although are the Slaters even Catholic?

No she didn't give birth in a 'Magdalen Laundry'

You don't have to be catholic

Unwed pregnant women were sometimes sent to these places to shield shame on the family and themselves.

Kat's not even that old though, so it's all a bit far fetched. I could however almost believe that Kat might have been sent away to protect uncle Harry because I imagine having a paedo in the family would cause some shame.