Since there's no further information, we will assume the trim she needs equals the sum of the perimeters of the three square pillows.
Then, since each pillow is 2 feet by 2 feet, the perimeter of each pillow, in feet, is:
2 + 2 + 2 + 2 = 8
Now, since she is making three pillows, the sum of their perimeters, in feet, is:
3 * 8 = 24
Therefore, she will need 24 feet of trim.