How do you say daughter of in Welsh?

The Welsh phrase for "daughter of" is merch followed by the father's name.

Here are some examples:

* Merch Dafydd - Daughter of David

* Merch Gwenllian - Daughter of Gwenllian

* Merch Siôn - Daughter of John

Note: The father's name usually appears in the genitive case, but this is often just adding an "-s" to the end of the name. However, this is not always the case, so be sure to look up the correct form for the specific name you're using.