I Have Had A Chow/Shepherd Mix For Three Months, And

I have had a Chow/Shepherd mix for three months, and about 1once a month she poops on the floor for about a day....it's bad, she gets dry food, good stuff 3 times a day and other than those episodes does exactly as expected. She has been vetted micro chipped the whole nine yards. What next? She know not too and shows remorse but it must be something I'm doing or not!? Help....