You've been here before but here is really hoping she makes three days and nights. I trust you will check her at night since sitting on the nest during daytime does not count. Only nighttime counts.
I don't know how many eggs your Brahmas are layiing now, but I would wait until I had a dozen. That is enough and not too many. She can easily cover more eggs but you still have winter in front of you. It would be nice if she could cover the chicks when they are three weeks old. With 12 eggs, you should get several to hatch. The way they spread their weight around, I would not worry about her smashing them as long as you have some kind of bedding in there. You can always candle them before you give them to her to see if you see cracks in the shell. That''s actually not a bad idea, but overall you tend to worry too much.
As far as reaching under her and all that. When I was a kid many decades ago (remember to respect your elders) one of my chores was gathering eggs. If we had a broody, I had to check under her every day. Some of those broodies were mean. I did not want to check under them. But every day I would grab them and throw them off the nest to see if another hen had laid under them. I did not want to grab some of those mean broodies, but I did not want to tell my dad that I was afraid of a broody hen even more. Sometimes you have to do what you have to do.