I think I would wake her up and get some fluid into her..it's important she is hydrated...and see if she will eat a little..
(the yogurt and food could possibly help neutralize any poison)
check under her wings for heat..
concerned about the color of the droppings.
an Avian vet is best, but any vet can do a fecal test for worms and cocci.
make sure the sample is fresh as possible.
it would be good if the vet could determine if there is something in the droppings other then just pooh..
(such as egg substance), or possible poison, or bacteria, such as E-coli, etc.)
these kinds of tests will cost more..but will help determine what course of action to take.
when she was on your lap yesterday..how was she? alert?
chickens will often hide that they are sick until very ill..
recheck her belly area for any swelling or heat.
do you have any antibiotics on hand?
link to information on Botulism..(just in case)
click here
click here for E-coli