OK...an egg in the oviduct has several regions it goes thru...so she could be in any stage.
Below is an illus I am working on. In the next day or so I will be adding type to it. But a quick summery of the times in each region.
Prior to an egg yolk entering the oviduct it is on a cluster of folicles (sp) which each bloom into a yolk (simple terms) that is delivers into the funnel opening of the oviduct.
1...Infundiibulum consists of celi that help to move the yolk down the oviduct. Several things occur such as: fertilization (sperm travels up the oviduct), the outer yolk membrane is added, and the chalazae in the string like thingys that suspend the yolk in the egg. transit time: 1 hour
2...Magnum, this region deposits the fluids which consists of albumen, sodium, (which is why hens will crave salt prior to laying), magnesium, calcium...this material makes up the white part of the egg. transit time: 3 hours
3...Isthmus, this region forms the inner and outer inside shell membranes. transit time: 1-2 hours
4...Uterus, which is also the shell gland. The egg will get some more salts, water prior to the shell being formed.Calcium is draw from the blood flow. transit time: 20-26 hours
5...Vagina, which is very muscular and will expell the egg from the body. While in this region a cuticle is added to the outer shell. transit time: seconds
After the egg leaves the body the cooler temps will cause the inner and outer inside shell membranes to separate up near the round end of the egg to form the air cell.
Hopefully this will give you an idea of what is going inside a hen during egg formation.
I am working on another illustration that will show the areas where things could go wrong.