When someones heart stops pumping blood around their body, the tissues and cells are deprived of oxygen and rapidly begin to die.
But different cells die at different rates. So, for example, brain cells die within three to seven minutes, while skin cells can be taken from a dead body for up to 24 hours after death and still grow normally in a laboratory culture.
From this point on, nature is very efficient at breaking down human corpses. Decomposition is well under way by the time burial or cremation occurs. However, the exact rate of decomposition depends to some extent on environmental conditions.
Decomposition in the air is twice as fast as when the body is under water and four times as fast as underground. Corpses are preserved longer when buried deeper, as long as the ground isn't waterlogged.
The intestines are packed with millions of micro-organisms that don't die with the person. These organisms start to break down the dead cells of the intestines, while some, especially bacteria called clostridia and coliforms, start to invade other parts of the body.
At the same time the body undergoes its own intrinsic breakdown under the action of enzymes and other chemicals which have been released by the dead cells. The pancreas, for example, is usually packed with digestive enzymes, and so rapidly digests itself.
The decomposing tissues release green substances and gas, which make the skin green/blue and blistered, starting on the abdomen. The front of the body swells, the tongue may protrude, and fluid from the lungs oozes out of the mouth and nostrils.
This unpleasant sight is added to by a terrible smell as gases such as hydrogen sulphide (rotten egg smell), methane and traces of mercaptans are released. This stage is reached in temperate countries after about four to six days, much faster in the tropics and slower in cold or dry conditions.
A corpse left above ground is then rapidly broken down by insects and animals, including bluebottles and carrion fly maggots, followed by beetles, ants and wasps.
In the tropics, a corpse can become a moving mass of maggots within 24 hours.
If there are no animals to destroy the body, hair, nails and teeth become detached within a few weeks, and after a month or so the tissues become liquefied and the main body cavities burst open.
I truly believe that she was placed somewhere in a protective covering (possibly buried), then moved to a different location, during that transport the protective covering was breached and that would explain the smell of decomp in the car, although the trunk is closed it is not sealed from the front compartment and the smell would migrate from the trunk to the inside compartment.
The body if buried and then moved would most likely leave trace amounts of soil in the trunk also. I think she left the car at Amscot because the smell was so bad that she could not stand it.
Often a body will be relocated to a different area, you have to remember that she is a CSI fan and although the stories they tell are not 100% accurate, they are also not that far off about body disposal.
At which point do you tie in the 2.6 days, that is the big question.