To a point yes, and as I understand it, to a point the increased fat will actually speed the set. But that is a lot of fat to try hold onto. It is important to understand that rennet is an enzyme and as such catalyzes a reaction but is not consumed during that reaction, they will eventually degrade but a small amount can do a lot, more won't nessesarily do more it will just do it faster all things being equal. I Just looked at the recipe, and yes she does call for equal parts milk and HEAVY CREAM, wow. I must have looked at that recipe 20 times and not noticed that. She does call for a 2 hour rennet set time before cutting, and a 15 minute rest after, she even calls for a gentle stir, GENTLE AND BRIEF might have been better to emphasize the fragility of this make. Truthfully I don't know if I would be brave enough to try this make, if I did I wouldn't cut the curd and I wouldn't stir, at all. I would spoon/ladle out and gently lay the curds in the mold the way some stilton makers do and let the cheese tighten up on it's own time, only attempting the first turning after it seemed to really firm up. I would also double up on the cal chlor, with goats milk maybe go to 3/4 tsp. People rave about the fat and solids content of goats milk but all the assays I have seen show it quite similar to cows milk, some goat breeds are supposed to give richer milk but most do not. Sheep's milk on the other hand is truly rich and that is what the original roquefort is made from. Sheep's milk is also naturally homogenized. But in no way do sheep give milk that would come close to the fat content of this make. I've used Mary's recipes as inspiration if not actually followed the recipe but this one is a bit weird in my view. Maybe it can be made but as you found out, it aint an easy one. Sorry you had bad luck with this.
Out of curiosity, was I right about the whey getting milky when you cut and stirred, and did it never clear up again?