You could call her Mac, Mackie, or Mickie instead (or go with no nickname). I've heard of little girls named
Makenna with the nickname Mak instead of
Kenna.
Makenna is a beautiful name imo, but I'm afraid that it's too trendy and that it will be eventually labeled as "dated". If this doesn't bother you, then go for it. I've run into two little girls named
McKenna (not sure on the spellings) this summer. I personally don't know of any others, but I don't know that many young children. It seems like
McKenna,
Makenna, etc. has gotten on the popular side.