I want to make my daughter for her birthday a "cake shoe" and I want to make the design her Nike shoes. I know that I can make it if not selling but question is from what I am reading about copyright and cake laws and rules is I can't post online the pics. Is this correct in this case or can I show my work online after finished? 

if you have  a cake business then no do not post it online to protect yourself from the copyright police and from potential clients who want the same design —

although I am not a lawyer — i would say it’s ok post online  if you do not have a business — but I do know of a teacher who used disney designs for her classroom walls that got her in trouble so... idk

I think the main reason not to post is so that others can’t try to get you to make one for them   As K8 said as long as you say it was for family it would be ok   

Thank you for your replies. What if I post online not showing the "Nike check" and just show the shoes? I think this should be ok, right?

yes I think so but if it is otherwise identifiable as Nike I wouldn’t