Between Monday and Sunday there are 7 days. If she will be using the same shirt for 2 days then she will need clothes for 7 - 2 = <<7-2=5>>5 days
Because she wants to use 2 different shirts each of those 5 days then she needs 2 * 5 = <<2*5=10>>10 shirts
In total she will need 10 shirts between Tuesday and Saturday and 1 shirt for Monday and Sunday = <<10+1=11>>11 shirts
#### 11