I have given eggs to setting hens that were partially incubated. They take to them just fine. I even had a hen that only set for 8 days before her chicks hatched. She didn't mind and was a great momma.
The easiest way I found was to take half the eggs she already has. Then set the new eggs...
You are keeping her from a clutch of eggs she has hidden somewhere. She will not be happy till she gets her eggs. If fact she is fighting mad.
My suggestion:
Get a open sided box or pet carrier ready with a nest. Let her out and watch. Most likely she will make a straight line to her nest...