Don, Slabs are going to crack, How much depends on alot of different things .
1. how much fill is under the slab.
2. What kind of fill is under the slab.
3. how much moisture is in the fill at the time of the pour.
4.how fast the slab dries.
And I could go on and on but there is no exact science on what a slab will do. When the slab is poured the mason makes a guess where the joints should be and how many there should be. Sometimes they get lucky and sometime they don't. When the rebar steel or steel wire placed where it should be the crack will not be a problem.Tell your wife not to worry and enjoy the house.
Hope this helps Donald Wood
On a lighter note, you could soak it in DNA and wait a few weeks
Turning makes the world go a'round