Hi Denise,
Portlaw is in the Civil Parish of Clonagam, Barony: Upper Third, Union of Carrick-on-Suir. I have checked Griffith's land and property valuations taken in late 1840's and I found a "Mary King" at No. 40, Knockane Road, Townland Coolroe with a House & Garden. No record for a Thomas King in Portlaw.
There are three others named "King" in Portlaw: Elizabeth - House, Office & Garden, John King - House, Office & Yard, John King, Carrick Road,Townland of Mayfield - House & Garden. You can access those records at - www.askaboutireland.ie - Free Site
In Roots Ireland I found a record for a "Mary King" whose parents are shown as Thomas King and Mary Donovan with the address: Tinaslee in the parish of Templeorum & Owning in the County Kilkenny. This parish is on the North side of Portlaw across the river Suir. Baptism: November 1st 1839. Sponsors: Michael Morohan/Monahan? and Margaret Tobin. I cannot find any record for this "Tinaslee".
There are a number of families named "Donovan" in the Portlaw area of County Waterford on Griffith's list.
If I come across anything further, I will post it to you.
Regards,