LadyMacca - I personally don't recommend you put her in a breeder net, as they can stress her out and cause her to abort. I'd advise you let her give birth in the tank, and some fry should survive if you have decorations and plants. As you find the fry, you can put them in the net to grow them up some, if you want.
If you really, really, want to....I'd say once she's been pregnant for at least 3 1/2 weeks. Even then, if she doesn't give birth within 3 days, take her out. 3 days is really the limit on how long they can be in there.
Yeah, ours could never stand even one afternoon in the breeding trap, they'd just mega stress trying to get back to the boys again. And the boys would be just as stressed in return. Total fish panic attack. I find a good clump of java moss usually hides babies really well. The ones too stupid to swim for cover end up lunch but the rest do just fine hiding out in the java moss. The female guppies seem to like giving birth around the java moss too, as if they know some of the babies will be fine in there. $4 a handful at our LFS.(for the moss I mean, not the guppies! )
Oh i am sorry for your loss how old was frenchy may he rest in peace i remember when i lost my favourite fish he was a betta his name was fliper I was about 8 at the time but i was pretty sad he died because he had a tropical fish disease i named him fliper my new favourite fish is called SHARK NOT A VERY THOUGHFULL NAME but he is now the best fish i ever had a nd i hope he lives a good life he is just ababy though
As far as the breeders go I only try to put the Mommies in if I see that the birthing is under way. I have had fish get stressed and try to jump out of the trap. One even managed to land on one of the support edges under the lid and if I had not been watching at the time it could have been a real mess!!!!!!