There are a few possibilities for why you might be thinking that:
* Confusion with another actress: There are other actresses named Pia who have been in children's programming, so you might be thinking of someone else.
* A guest role: While Hamilton wasn't a regular character, she may have played a guest role in a single episode. It's also possible she was part of a stage production of "Barney & Friends" or a related project.
To help clarify, can you provide any further details about the character you are thinking of? For example, do you remember anything about their appearance, their role in the show, or any specific episodes they were in?