I think we are going to need more information!
There are lots (20+) Olwen Jones in Merthyr Tydfil on the 1911 census - but none of them has a father Isaac.
There are quite of few Olwen Jones, with a father Isaac, but none of them in Merthyr Tydfil.
The combination of Jones, with a forename Olwen isn't exactly uncommon!

Do you know when Olwen married and/or died?