
As Megan said Companion Dog Shows are supposed to be for dogs of 6 months and older (but no KC reg stuff to worry about) however most people take younger puppies along as a way of socialising them with lots of other dogs, people and getting used to the strange noises etc so at 5 months you'll not have the only young puppy there. You can of course inform the steward/person taking the entries that your pup is only there for the practice and you are not looking to have her placed but you'll almost certainly find that they hear that a dozen times so it's unlikely to be a problem ;)
If it's not advertised as a Companion show and just a Fun Dog Show (which is what you mentioned) the 6 month rule doesn't apply anyway :)
Re the kaolin on her ears (didn't know that was something put on ears

) however you could try removing obvious evidence with baby wipes first.
Good luck and more importantly enjoy the experience - it's a good way of picking up some useful info as well as vibes. Teri :)