To determine how many cups of sugar were left in the mixing bowl after NeNe spilled some, we first need to find out how much sugar NeNe had after tripling the original recipe.
The original recipe calls for 5.25 cups of sugar. NeNe tripled that amount:
\[ 5.25 \text{ cups} \times 3 = 15.75 \text{ cups} \]
Next, we find out how much sugar spilled from the mixing bowl:
\[ 4.46 \text{ cups} \]
Now, we subtract the amount that spilled from the total amount of sugar NeNe had:
\[ 15.75 \text{ cups} - 4.46 \text{ cups} = 11.29 \text{ cups} \]
So, the number of cups of sugar left in the mixing bowl is:
\[ \boxed{11.29} \]
Thus, the correct answer is option A: 11.29.