Any laying bird may growl when you reach under her in the nest...
....and also will tuck an egg under.
Here are my go to signs that a bird is broody:
Is she on nest most the day
and all night?
When you pull her out of nest and put her on the ground, does she flatten right back out into a fluffy screeching pancake?
Does she walk around making a low cluckcluckcluckcluckcluck(ticking bomb) sound on her way back to the nest?
If so, then she is probably broody and you'll have to decide how to manage it.