It is indeed a combination of factors. Personal skills, experience and professional qualifications must be considered. It important to understand that the Supreme Court of Canada is a court with general jurisdiction. One should always look for judges who are able to exercise expertise in a variety of areas.
You are absolutely right to point to Justice O'Bonsawin's expertise and experience in the field of mental health, especially with respect to the principles the Supreme Court outlined in the Gladue decision. This is a very important aspect of everything we need to consider for the country, as well as for criminal law.
Justice O'Bonsawin also has experience in the areas of labour and employment law, human rights and privacy law. She brings a range of experience to the court. All of that must be considered.
I believe you have done so yourself, but I encourage all Canadians who have not already done so to review the nominations that have been submitted, which are in the public domain, so that they can see what candidates who aspire to be Supreme Court justices must submit and what criteria they must meet.