Aisha Esbay says she approached Lambert for a picture, only to have Lambert refuse. After Esbay's friend was similarly rebuffed, Esbay confronted Lambert.
"I asked her why she was so rude," Esbay tells PEOPLE, "and she started yelling these hurtful things at me."
Esbay alleges that Lambert pushed her multiple times. A publicist for Lambert had no comment on the allegations.
The Smith County Sheriff's Department is investigating the incident.