Is my daughter eligible for CAI if she is a student in Toronto during the year but her main residence is Sault Ste. Marie?

Yes. If she is 18 years old or older, and lives in Ontario, and there is nothing else that disqualifies her, then she is eligible for the CAI. If here primary residence is outside of a CMA, then she might qualify for the Small/Rural Community Supplement.

This CRA webpage has more info on who is eligible for the CAI: https://www.canada.ca/en/revenue-agency/services/tax/individuals/topics/about-your-tax-return/tax-return/completing-a-tax-return/deductions-credits-expenses/line-45110-climate-action-incentive.html#Eligibility

This CRA webpage lists what is considered part of a CMA (Ontario is at the bottom): https://www.canada.ca/en/revenue-agency/services/tax/individuals/topics/about-your-tax-return/tax-return/completing-a-tax-return/deductions-credits-expenses/line-45110-climate-action-incentive/qualify-for-the-supplement.html