I was thinking about that.You're probably fine leaving them under her for right now but I would definitely crank up an incubator to finish the hatch in. Even if your broody is willing to sit in the nest a bit longer you don't really want her staying in the nest longer than a few days so she gets up to start tending to the already hatched chicks.
After I have a hen to hatch I always move them to a cage with the babies so they can eat and drink without the other chickens around them. My last broody still had one egg after I moved her and it hatched 2 days late, I think she would still be sitting on that egg if it wouldn't have hatch lol.
I marked the 2 I put under her today so I will just have to wait now and see how it goes I guess.