Answer:
6 connecting cubes
Explanation:
Finding rectangular models in two ways is nothing but factorization of a number in two different ways.
Note that 6 is the minimum number with two different factorization 1 x 6 and 2 x 3.
There is another number 4 (< 6) with two different factorization 1 x 4 and 2 x 2 but 2 x 2 will give a square model.
Hence, using 6 connecting cubes, Emily can make one rectangular model with dimensions 1 x 6 and another with dimensions 2 x 3.