Can I use "covered with" instead?
Cover in/with/by seem to have similar meanings but there are slight differences in usage. In this case, Peppa is covered in mud but she is still visible. When you are referring to being covered by something (like a substance like the mud mentioned in this video), it is more appropriate to use "covered in." This indicates that something is being widely covered, but has not completely disappeared from view. Ex: My son's face is covered in jam. When you are referring to a covering that actually hides the thing being covered, "covered by/with" is more appropriate. Ex: The field was covered with snow. Ex: The child was covered by blankets.