Spears, 25, stopped by the San Fernando Valley salon at around 7 p.m. Friday night after it had closed, Tognozzi tells PEOPLE.
Accompanied by two bodyguards, Spears walked in with a hoodie covering her head and told Tognozzi, "'I want you to buzz my hair off.'"
Tognozzi first tried to talk Spears out of going through with the shave, then after refusing the pop star's request, Spears told her, "'Then I'll do it.'" (Click here to see the photos.)
During Spears's visit, which came after news of her short rehab stint broke, Tognozzi describes the pop star as having "no expression." However, she notes Spears smiled for the cameras when waiting photographers caught sight of her newly shorn look inside the salon.
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Before Spears slipped out the back door, Tognozzi asked her if the buzz cut was a symbol of a new beginning. Spears's response: "'Something like that.'"