No one has a right to play soccer for a private team. If she's actively undermining her sponsor, why should they support the team? It'd be like Dale Jr. saying on TV that he exclusively drinks Coke products even though he's sponsored by Pepsi. The soccer player wasn't being forced to eat the fish, she probably wasn't asked to speak publicly about her love for the fish, the article said she and her mother (probably mom's fault TBH) were interfering with the sponsorship agreement just because they personally did not like the fish and therefore have some kind of dignity interest in demanding that what they don't like goes away. Yes, you can protest, but don't expect some guarantee against retaliation, especially with something as trivial as a private children's soccer league.
Yep, Corporation's rights and corporate advertisements come before children.
The fun of all the other children who get to play soccer because a team exists come before one mom's weird grievance with penned fish.