I like
Ffion.
Ceridwen is okay, but I'd pick a different middle name.
If you want the middle name to be Welsh too, then I like
Ffion Eira or
Ffion Mererid.
But otherwise, I like
Ffion Agnes,
Ffion Ginevra, and
Ffion Eleanor. I think it needs a more feminine middle name since it looks similar to, and therefore makes me think of, the male name
Fionn.