You would check the crop first thing in the morning before you give her anything to eat/drink.I live in Memphis TN. How am I going to understand if crop is emptying? It feels soft and squishy. Her mouth is open and has a difficulty to breathe.
How long has been having trouble breathing? Anything stuck inside her beak, lesions in the throat?
Any bloat or fluid in the abdomen?
She's in crisis, so you're going to have to access her.
Have you ever had respiratory illness in your flock?
Can you feel an egg inside her vent?