Your wife's California residency status is determined by California tax law. It is not a matter of choice. This reference gives California's detailed rules for determining residency status:
https://www.ftb.ca.gov/forms/2020/2020-1031-publication.pdf
Note: A non-resident return (CA Form 540NR) is required by CA when a resident spouse and a non-resident spouse wish to file a joint return.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
