Ava and
Caoimhe don't sound anything alike in my accent. KEE-va and AY-va. And I really don't see why you should be mad at your cousin, she had the child first, what was she supposed to do say "well, I really love
Ava but can't use it because my cousin may call her child
Caoimhe in a few years time", sorry if that sounds harsh but its what I feel. If you love
Caoimhe then you can still consider it, because even if they were rhymey they wouldn't get confused all the time as they do not live together, and may not even see eachother all the time if they are second cousins.