Since she spent 360 days of the tax year in CA, per California law she must file her CA tax return as a resident. See the California FTB reference cited in my previous post.
Her filing in MA will depend on her residency status there as defined by Massachusetts law. This web reference will give you the details on that:
https://www.mass.gov/service-details/learn-about-legal-and-residency-status-in-massachusetts
Residency for tax purposes is not a matter of picking and choosing. Each state has specific laws regarding such residency.
Note that a taxpayer may be both a domiciliary resident of one state and a statutory resident of another, a situation known as dual residency.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
