Welcome to the forums!
Before taking the breeding route and in order to do so more safely, a person should have a very good grasp of the species (this comes with real life experience in budgie ownership) and to do the required research into the subject.
The decision to breed comes with a whole lot of responsibility and commitment, the lives of the breeding pair(s) and the chicks are depending on you and the response you give if/when faced with adversity.
Things like being able to tell if your breeding pair is in good health and top physical condition to go through breeding; when a hen is expecting an egg or if she is showing the first signs of being egg bound; when a chick is having developmental problems, not being fed or showing signs of dehydration;
when there is aggression, abandonment and neglect of the chicks and it's solely up to you to feed and raise the chicks. The ability to detect early on and solve these issues can truly make a difference on the outcome of your breeding journey.
Please read this link: https://talkbudgies.com/budgie-breedi...s-new-old.html
Given Shirley's temperament, it's not advisable to allow her to proceed with breeding. Budgies that display a more dominant behaviour and consistently bully their mates and get into fights aren't the most suitable ones to breed, because with the hormonal changes, the bad temper can escalate quite badly and the chances for the breeding venture to end in tragedy for the father budgie and any potential chicks are much higher.
The best thing to do given the circumstances (and the fact that you are not fully prepared to raise the chicks in case the parents prove unfit) really is to discourage further breeding behaviour and to take the required steps to get your female budgie out of breeding condition and to break her egg laying cycle.
In order to accomplish this, it's best to move Shirley (and separate her from her mate) into a spare cage and do not give her a nest box, a hiding place nor anything that she can use as a nest.
For the detailed information, follow the recommendations on this link: https://talkbudgies.com/budgie-breedi...want-eggs.html