I love that you are looking for a unique name, but I'd stick to more traditional spellings. As someone who has a last name that is unpronounceable to most people (even though it seems obvious to me), I can tell you that correcting people gets really old. I can't imagine how maddening it would be if my first name gave people problems!
Of the two, I'd choose Kuinlynn, but I think your daughter would thank you if you spelled it with a 'Q.' It's still unique, and sounds good phonetically with your other daughter's name, but imo is nicer because it is less matchy. But just my opinion. Sorry, I hope I haven't offended you, I know names are hard!