I bought 25 cornish cross, 21 of which survived to processing at 5-9 weeks. I put them in a 10x16 open air covered run at 4 weeks old, and I think I could go down to 10'x15' but less than that I don't feel like they'd have enough room. Others may disagree with me, but I think 25 CX in 48 sq feet (6x8 shed) is too small. Also, it's a heck of a lot more work to deal with the poo. So that's one thing to keep in mind if she does this again.
It took me a very long time to process those 21 chickens. I started at 5 wks, and processed every day after work (1-2 chickens an evening), and on the weekends (4-6 a weekend). It took till they were 9 wks old before I was done. Granted, I don't have an automatic plucker, and after the first seven I skinned them instead of plucking (it was faster and I don't eat the skin much anyway). Took me 1.5-2 hrs per chicken from coop to ice chest, and it was just me doing it.
One thing I'd recommend is that since they're so large, when she goes to process them, part most of them out. The breast meat is so large compared to the leg meat, by the time the breast is cooked, the legs will be way overdone if she tries to roast these. Maybe do a couple roasters just to see, but you'll probably be dealing with raw and overdone chicken all on one bird. Or you could pressure cook them - that would make sure everything gets cooked properly. If you cut apart the thighs, breasts, legs, etc, then you can package them into family size portions, and put similar thicknesses of meat together, for easier cooking.
I'd start processing them immediately. The longer she waits, the more will die. They are way past due. Unless you can commit to processing no later than 8 weeks, a slower growing broiler would probably be a better choice than CX.
If them having dirty feathers is an issue, one thing I do is give mine a post-mortem bath. I hang them up by their feet, wet them down, and rub them all over with dish soap. This helps remove some of the dirt and grime before I either pluck or skin them.
Good luck to your friend. I think she can still salvage things. Hopefully next time she'll plan things better.