Odd situation. Broody hen?

So first off, I have two flocks. One flock (Flock A) has a rooster, but all the hens eat their eggs. The other (Flock B) has no rooster, but they lay fantastic eggs.

So today I put 3 golf balls in Flock A's coop, to see if I could get one broody. My one eyed lavender Orpington hen ran in, sat down on them, gently rolled the eggs under her with her beak and fluffed out. She slightly spread her wings as well. Hopefully she stays put. I let the other hens and my rooster out to free range and closed her in so she would have privacy and get the mother mind set on.

Now, for eggs! I can't collect the eggs fast enough from flock A before they eat them, but their eggs are fertile because of my rooster in with them. If I put my rooster from Flock A in with Flock B, how many days should I wait to collect the eggs so I know they are firtile?

Weird. I know! If all else fails I'll order hatching eggs, but I'd rather not. And if she gives up on being broody then it's all just a big bust.

I also wanted to add that once she's stable and fully broody, I would move her out of there so they other hens don't eat the eggs. That would be a disaster!

Maybe you could begin by trying to dissuade egg-eating (try typing it in the search box and seeing what pops up).

This link may help you to determine if an egg is fertile

https://www.backyardchickens.com/t/16008/how-to-tell-a-fertile-vs-infertile-egg-pictures

Best of luck

CT