Pecking orders are fluid and change all the time - due to brooding, illness, isolation, etc. It's not true that a hen lower in the pecking order won't be able to protect her chicks. It's very individual, of course, but on the whole, broodiness puts the pecking order on pause and gives the broody hen extra balls to fend off anything endangering her chicks. She goes into mama bear mode. The flock should know to stay away from a broody and her babies, regardless of her previous place in the order. When the broody cycle ends and she weans the chicks, she may return to her previous place, or she may take advantage of the situation and enjoy a more permanent upgrade. That's what happened to my star broody and best mama. She started out very low in the pecking order (second from the bottom), but held her own during her maternity and liked it so much that she refused to go back to her old place. She ended up settling in the middle. And she keeps getting bolder with each round of chicks she raises.