The Alberta Court of Appeal has found no fault in the three years handed to Tatyana Granada after she was convicted in 2012.
Her lawyer had argued that the sentence was harsh and excessive for a first conviction.
The sentencing judge said Granada showed a reckless disregard for community safety.
The food tampering began after Granada had been charged with shoplifting at the store and barred from it and all other Co-ops in Calgary.
Co-op estimated it lost at least $600,000 in business and in costs associated with the investigation.
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