It seems most likely that ...
... Samantha will save $37.50 because she must first find the 25% sale price before taking the extra 50% reduction
_____
In the real world, it seems probable that Samantha will be offered the choice of using the coupon or the sale discount. If she chooses tht 50% coupon, her savings will be $30. If she chooses the marked sale discount, her savings will be $15.
The scenario above assumes she gets 50% off the sale price of $45, so saves $15+22.50 = $37.50 off the original price.