You can candle the first broodies eggs to see if they have veining still, are dead, or are internally pipping.
It really depends, but yes. I wouldn't let a broody sit for two months straight if a first batch didn't hatch, or let her sit at all if you don't plan on letting her hatch anything...
Over month is too long if she doesn't have anything hatching. You can candle the eggs on day 7-10 and look for veining. Any that are empty can be thrown out so they don't explode.