.. So basically diet and exercise will help? XD that's awesome! I did want to cull her.. but she's so friggin awesome and they seem to be sooooooooooooooooo attached!
Buff Orpingtons are wonderful birds that are great layers and docile pets, not exactly the best meat birds though. Cornish Cross are a completely different thing. Tuff is definitely a Cornish Cross. They must be kept on a strictly regulated diet for life, and exercise is a must. Start limiting Tuff's access to feed to just having access to it during the day. And keep it as far from the water and the heat source as possible. The idea is to make her move as much as possible to meet her needs. At 6 weeks, limit her to just 2 feedings a day, in the morning and evening. And get them out on grass as early as possible to encourage foraging.
Something I learned from a friend who raised a dozen Cornish X for fun -- if the birds are kept outdoors in a heatwave it is best not to keep the water too far from the feed. These birds can literally die of thirst because they won't move the 10 steps they need to get to the water. I feel so sorry for these poor babies. They grow so fast their skeletal structure can't support their fast and massive muscle or internal organ growth thanks to man's gross engineering of this poor breed. Sometimes they die from pain and suffering before they reach 2 months. They are fed continuously in the poultry industry to make them grow fast so it stands to reason to feed your chicks on a more sparse schedule to eliminate getting them to grow too heavy too fast. Sometimes Cx's that are overfed or not on a strict diet just rest themselves in front of their feed and water and don't move the whole day. So sad. Crows pecked and killed 1/2 my friend's Cx chicks through the pen wire because the chicks were just leaning on the side of the cage too heavy and lethargic to move.