I think the goo would just be discharge? Unless she passed the mucus plug, which would be impossible to know, does her side seem smooth straight to the hip? Or is she sunk in, in front of the hips?
The biggest thing I look for is, a full udder, a very relaxed, almost falling open vulva, a V shaped Belly, and sunk in sides, as well as wax. I would say if she is showing any combination of 3 of the signs, then I myself would be doing nightly checks.
Baby, Sparta, Carmen, Henry, Hooch, Mercedes, Butterscotch