I don't particularly like it because despite the popular British actress
Glynis Johns (star of films about 40-50 years ago) I associate it with my elderly cat-hating neighbour! I think there are prettier Welsh girls' names beginning with G or with the -ys ending.
However, it has the merit of relatively uncommon and therefore probably not associated too much with a particular era.
If you stay with a Welsh theme how about
Glynis AngharadGlynis BethanGlynis BronwenGlynis Rhiannon