I'm going to assign each skirt a letter and each pair of shoes a number:
Skirt A, Skirt B, Skirt C
Pair 1, Pair 2, Pair 3
Now, I'll put them together into skirt/shoe pairs:
Skirt A and Pair 1
Skirt A and Pair 2
Skirt A and Pair 3
Skirt B and Pair 1
Skirt B and Pair 2
Skirt B and Pair 3
Skirt C and Pair 1
Skirt C and Pair 2
Skirt C and Pair 3
Altogether, there are 9 skirt/shoe pairs. So, Amanda could create 9 different outfits.