I just hate breeder nets, so the answer to this question is no. But if you want to save all the fry, wait until she starts giving birth and then scoop her in as soon as you see her. The fry maybe so small that you won't see them and normally hide well in the gravel so you need a trained eye. If you breeder net doesn't have a divider for the fry, she will still turn around and eat some fry more than likely and they have no chance in a box that small.
She will either start racing the tank glass up and down while giving birth, or she will isolate herself somewhere but would come out from time to time to join the rest. It depends..