An Extra Shadow

Yes, an extra shadow is what I have...and her name is Mackenzie.  Does anyone else have a kid(s) who ALWAYS has to be by your side or in your arms?  Kenzie has tons of toys...none of which she plays with.  Apparently, she would MUCH rather follow me around and whine wanting me to hold her.  It pretty much makes it impossible to get anything done around here.  She's also going through a violent stage (I hope it's just a stage).  She's constantly hitting & pinching me!  If I smack her hand and tell her "bad" she laughs and hits me back!  Any advice on how to get her to be more independent, less whiny & non-violent?  PLEASE?!?!