ok, its possible, ANYHTING is possible...... but lets be realisitc.
courtney is far far inferior to billy in terms of musical ability. its comes freer to him.he doesnt need anyone to help him write a song and he's sure written and arranged far more songs than she has. he's a consistent player of instruments, meaning he never loses his grasp of musical structure and the mroe you play HANDS ON, the more you learn about music.
shes a dependent song writer while he's an independant one. i dont exactly fall all over him or anything but theres no denying it. sure she has creative ideas, but to write phrasing for a song that he wants to copy? WHY? he can write ten songs for her one. shes a PERSONALITY who happens to collaborate on music, some of which is good its her main output I GUESS but shes not neccesarily a hardcore prolific musician, she has alot more interest in being a personality more than anyhting.. he on the other hand is a singer/ songwriter/ guitar player without too much of a personality *in my opinion*
this is SO unlikely.