Guineas are not chickens and do not act like chickens. They are a flock bird and do best in large groups with other guineas. If imprinted by other poultry, they do not play well with them.
I brood and raise my guineas separately from my other poultry. I also house them separately. I went...
Read the thread Raising Guinea Fowl 101 and pay particular attention to posts by @PeepsCA .
If it was me, I would not take in a keet with a slipped tendon nor would I ask someone else to take on the burden. If it was mine, I would have culled it.