Last Sunday a car parked up a driveway in Harpham Rd was set alight and gutted.
The incidents have led to fears a serial arsonist was at work in the area, although police have yet to draw a link between the two incidents.
Ms Mortensen has lived at her Osier Rd address for about a year and said it was quiet, a great place to be and that there had never been any problems.
Until 3.20am when she heard the horn of her car blaring. "That was all I heard."
She went to the window to see what was happening and witnessed her car blazing - the flames having set the horn off.
The fire service had just arrived as they were already in the area attending two other deliberately lit fires.
The first fire was reported at 3.18am in Meeanee Rd and involved rubbish bags being set alight.
While firefighters were dealing with that a second call came in just two minutes later - rubbish had also been set alight in Guppy Rd which intersects with Meeanee Rd.
Just eight minutes later the third call was received - a car was on fire in Osier Rd.
"I was afraid it would blow up. I'd three-quarters filled the tank that day and it was just all going up," Ms Mortensen said.
She gathered up her son and got away from the house - heat from the fire blistering a tree and bushes out the front.
"I was just shaking ... I just felt sick."
Her brother had been staying the night and had his car parked in front of hers. It received only slight blistering.
She said her only consolation was that her car was insured.
"They have to get these sort of people or they'll just keep doing it again and again because they think they can get away with it. It's just sicko stuff."
A firefighter at the scene said the distance between the three fires, and the timing of them, indicated the offender or offenders were likely to have been in a car.
Napier police Senior Sergeant Sarah Stewart said police wanted to hear from anyone who saw or heard any unusual or suspicious activity in Osier Rd early Thursday morning.
As Ms Mortensen watched the remains of the car being taken away a neighbour three doors away arrived and said if she needed to get shopping or be taken somewhere she would happily drive her.
"That's really nice," Ms Mortensen said. "There are some good people out there."