Dear Brother, Salaam Alaykum.
For your knowledge, it is not the duty of your wife to financially support your parents from her gifts or earning. If she does so willingly, then that is fine.
Financial support to parents when they need it is as important as fulfilling the basic rights of your wife (basic and necessary provisions).
It would be unethical to request for refund of the money given to your parents.
You could explain to her lovingly the need (in the past) and benefits (generally) of supporting your parents in any way possible. You could reassure her that you care for her as much as you care for your parents and also explain to her that keeping a positive, comfortable and caring relationship with your parents will ensure a happier family especially with your children (their grandchildren).
You will need patience with her in order for her to calm down and develop good feelings for your parents.
May He guide us all with our relationships.