Simplify the following text for a Grade 11 native English-speaking person.
Original: Nyssa was created by writer Johnny Byrne for the Fourth Doctor serial The Keeper of Traken , but the production team subsequently decided that she should join the Doctor on his travels .
Simplified: Nyssa was created by writer Johnny Byrne for the Fourth Doctor serial The Keeper of Traken , but the production team later decided that she should join the Doctor on his travels .