The anonymous letter was addressed to Carlotta Flores, who owns El Charro Cafe in Tucson.
"I just think it is nice that she knew that she had done wrong," Flores told Inside Edition.
The letter indicates the former waitress stole from the restaurant 20 years ago.
"One of the waiters I worked with had encouraged me to 'forget' to ring in a few drinks a shift and pocket the cash," the letter read. "And for some stupid reason, I did it. I grew up in the church, I knew better. I hadn't stolen a dime before then, nor have I since."
Flores said she was surprised to receive the note.
"I was shocked and little bit in disbelief that anyone would take time to send a letter of this nature," Flores told Inside Edition. "This was definitely a letter of remorse and penance and going forward and that is exactly the way I accepted it."
The letter, signed "a thankful former employee," concluded: "It’s been 20 years, but I still carry great remorse. I am very sorry that I stole from you. Please accept my apology and this money as a repayment and 20 years of interest. May God forever bless you and your family."