Ok, I think my husband and I have it down to the above three for a girl, after much chaffing and changing-of-minds.
Just to clarify re gender suitability etc:
Auden is allegedly technically a boys' name but this doesn't bother us as it just seems waaaay more feminine than masculine.
Corin is unisex - according to the ONS, there were 9 boy Corins in 2012 and 8 girls. We aren't keen on Corinne or Corrine, due to pronunciation confusion.
Merryn - to me this sounds feminine, especially with the nn Merry (discounting the hobbit...)
Which is your preferred option? Ay other suggestions along similar lines? Middle name is likely to be Grace.