Anderson was unofficially told that she made it on the team after the semi-final. The official field was set after Anderson's official DQ by referees who reviewed the tape and ruled that her DQ was justified. This happened late Friday night.
Again, the official field was set. Alice Schmidt was officially told she was the 12th qualifying runner. This field of 12 was running the final on Sunday no matter what.
The only question was whether Anderson could appeal to be added to that field. She was reinstated the next day. Thus, 13 runners in the final.
It's more than just USATF told Schmidt that she made it in and now they can't take it back. They selected an OFFICIAL field for the Olympic Trials for the final of the women's 1500. They can't take that back. They followed their established procedures in selecting the official field knowing full well that if an appeal was successful they could just add Anderson to the field The difference between 12 and 13 runners is negligible.