should restaurants make waitstaff pay when a table runs out on their bill?

[I am me And no one else]

My sister is a waitress and some dumba** with teenage kids had a $50 bill and literally RAN out of the restaurant, leaving my sister to use all her tips to pay for their dirty deed. She only makes 2.13 an hour and most goes to taxes. Her checks average about $10 a week. It is true that waitstaff live off of tips. Is it right that many restaurants have this rule?
It's very common for waitstaff to make well below minimum wage because the tips they recieve are supposed to offset it.