I thought it was a feminine singular that caused "gwaetha" to mutate - so does that mean Morgan has undergone a sex change, or have I missed something else?
Really? Pardon my ignorance. I'd only ever encountered it as a man's name.
It's normally a male name in Wales (and the rest of the UK) but often female in the US (eg Morgan Fairchild). Sometimes British parents will copy American usage and use a name for the "wrong" sex. Isn't it great that the mutation in the Welsh for "Morgan is the worst" gives the reader the extra information that this Morgan is a girl or woman!
Hence my original comment - but I have now looked up Morgan Fairchild (at first I thought it was a name you'd just made up).