If you look at Dream Supreme's final two races you can make a case that her assigned weight was the reason she lost.
In the Ballerina(G1) she visibly tired in the stretch, giving 9 pounds to the winner Shine Again, and finishing 3rd, 2 L back.
http://www.equibase.com/premium/eqbP...try=USA&race=9
Her final race, 2 months later in the First Flight(G2), saw her giving 5 pounds to winner Shine Again in a 2nd place finish by a head.
http://www.equibase.com/premium/eqbP...try=USA&race=8