It's possible that:
* Her name is misspelled or the name is not a stage name.
* She has worked on smaller, independent projects.
* She is primarily active in other areas of the entertainment industry (like theatre or voice acting).
To find information about a specific person's work, you can search for them on:
* IMDb: This website is a great resource for information on actors, directors, writers, and other film and television professionals.
* Wikipedia: While it may not have information on everyone, Wikipedia is a good source for biographical information and career details.
* Other industry databases: Websites like Allmovie, AllMovie, or even a simple Google search can sometimes turn up additional information.
If you have any other details about Sonia Madoc, such as her age, location, or the type of work she does, it might be helpful to include that information in your search.