In Australia a spayed dog cannot be showin in confirmation, I am sure the rules would be the same in the States. Not sure about Canada though.
The original purpose of a dog show (in fact, most animal confirmation shows, really) was to determine, promote and evaluate quality breeding stock for each breed of animal. If you look at it from primarily this perspective, it makes no sense whatsoever to show an altered animal, as they can never be bred.
You would be able to trail her (obeidience, utility, tracking etc). I am sure you would find it a lot of fun too and not so political
There maybe some shows that allow 'altered' dogs, i am not sure though.