Your mother can only be claimed as a dependant on your tax return if you are supporting her and she meets the qualification of being "infirm".
Starting in 2017, the Canada Caregiver Amount has replaced the family caregiver amount, the amount for infirm dependants age 18 or older, and the caregiver amount. While in previous years you could claim a credit for a parent who wasn't "infirm", to get the new Canada Caregiver Amount, you must have either a signed statement from a medical practitioner or a Form T2201 on file with the CRA.
More information can be found on the CRA website:
https://www.canada.ca/en/revenue-agency/programs/about-canada-revenue-agency-cra/federal-government-...