The court heard she struck her victim repeatedly in the head with the hammer, causing serious injuries and breaking her wrist as she tried to defend herself.
The pair had worked together since 2017.
Neighbours rushed to help the injured woman and gave her first aid, while placing the hammer in a plastic bag to so it could later be forensically examined by police.
Smith later texted a friend and wrote: “I’ve done it – I’ve smashed her head in -Oopsie xx!”
She also outlined plans to “go on the run” in Liverpool.
But she eventually handed herself in at a police station and was arrested on suspicion of attempted murder.
She was also sentenced for possessing an offensive weapon, an offence she had admitted, and given a restraining order banning her from contacting the woman.
Det Con Stephen McNee said a “violent woman had been take off the streets”.
Smith’s boss had suffered life-changing physical injuries that “may heal but the mental trauma of the attack will stay with the victim for life”, she said.
“I’d like to thank her for her bravery in supporting us with our investigation.”
