"It was her birthday on the Wednesday and she came in like normal. She didn't come in for a few days and then she didn't come in on Saturday like she always does, but I thought perhaps her cousin from Chelmsford was visiting her," Congrave, 39, told the Southend Echo.
Congrave then took it upon herself to call the police after Mann failed to show up at the beginning of the following week.
"On the Monday she didn't come in and the best thing I did was call the police because I was concerned and luckily I had her address so the police went to check if she was ok," Congrave said.
Police arrived at Mann's home to hear her shouting for help as she had been stranded in the bathtub for four days.
"I went to turn over onto my knees to get out of the bath, and I couldn't. My body wouldn't turn over," Mann told the BBC. "I don't understand how calm I kept. It wasn't natural. Something kept telling me 'keep calm.'"
Mann had managed to survive by refilling the tub with hot water, drinking water from the tap and covering herself with bath robes and towels.
Congrave said Mann had given her a house key and she planned to buy the beloved customer a cell phone and check in on her periodically.