Jacquetta Simmons of Batavia was sentenced in Genesee County Court on Wednesday.
A jury found Simmons guilty of felony second-degree assault in August.
Store security video shows the 27-year-old Simmons knocking Grace Suozzi to the ground with a punch to the face when Suozzi asks Simmons to show her receipt on the way out of the store.
Simmons could have received up to seven years in prison under New York's so-called "Granny Law." The law makes it a felony to intentionally injure someone age 65 or older if the defendant is at least 10 years younger than the victim.