There is no true and tested way to determine accurately if she will not pop out more babies.
A male guppy will fertilise any female guppy it is in with. Mother,sister, no relation, whatever. It doesn't know and it doesn't care. That is nature.
The female gets a deeper tummy and there is a dark (gravid) spot by her anal fin.
Guppies don't really "like" other guppies. They are pretty stupid animals offense to you guppy lovers. All they do is breed.
If there is a female guppy and a male guppy in a tank you can almost guarantee the female will be gravid ( pregnant ).
The best way to tell if a skeleton is male or female is to inspect the pelvic area. On the male it will be narrower (it will look like a nice butterfly shape) on the female it will be wider. This is so for birthing. there are other subtle differences but this is the best way to determine the sex of a skeleton.
A guppy will be small ish and very colourful, with colour all over the body for males and on the tail for females.
When the female stops laying eggs and the male stops fertilizing them.
if they have a black dot on there belly
slap them with a fish then youl know
I don't know why; I'm not a guppy-whisperer, but as far as I know, it is normal. Be careful though. It shortens the life of your fish.
Only a veterinarian would be able to exam your ferret if she's having problem with birthing. If the female ferret seems in distress or in pain, contact a veterinary immediately.
See the people at your local hospital birthing unit, they will know.