How long ago?
Does she still have Provincial Health card, driver's license,bank accounts, house, RRSP,club membership, children under the age of 18, file any income tax returns, how often did she return to Canada and where did she stay when returned to Canada.
https://www.canada.ca/en/revenue-agency/services/tax/international-non-residents/information-been-moved/determining-your-residency-status.html
Determining your residency status
Under Canada's tax system, your income tax obligations to Canada are based on your residency status. You need to know your residency status before you can know what your tax responsibilities and filing requirements to Canada are.
To determine your residency status, all of the relevant facts in your case must be considered, including residential ties with Canada and the length of time, purpose, intent, and continuity of the stay while living inside and outside Canada.
The following steps can help you determine your residency status for income tax purposes and your tax obligations to Canada.
Step 1: Determine if you have residential ties with Canada
The most important thing to consider when determining your residency status in Canada for income tax purposes is whether or not you maintain, or you establish, significant residential ties with Canada.
Significant residential ties to Canada include:
a home in Canada
a spouse or common-law partner in Canada
dependants in Canada
Secondary residential ties that may be relevant include:
personal property in Canada, such as a car or furniture
social ties in Canada, such as memberships in Canadian recreational or religious organizations
economic ties in Canada, such as Canadian bank accounts or credit cards
a Canadian driver's licence
a Canadian passport
health insurance with a Canadian province or territory
The information above is general in nature. For more information on your residential ties, see Income Tax Folio S5-F1-C1, Determining an Individual's Residence Status.
Step 2: Determine your residency status and its tax implications
Your residency status if you left Canada
If you are working temporarily outside Canada, vacationing outside Canada, commuting (going back and forth daily or weekly) from Canada to your place of work in the United States, or attending school in another country, and you maintain residential ties with Canada, you may be considered a factual resident of Canada
If you left Canada and established a permanent home in another country and you severed your residential ties with Canada ceasing to be a resident of Canada in the tax year, you may be considered an emigrant
If you established residential ties in a country that Canada has a tax treaty with and you are considered a resident of that country, but you are otherwise a factual resident of Canada, meaning you maintain significant residential ties with Canada, you may be considered a deemed non-resident of Canada. The same rules apply to deemed non-residents as non-residents of Canada
If you left Canada and you are a government employee outside Canada, which includes members of the Canadian Forces posted abroad, you are usually considered a factual resident or a deemed resident of Canada. For more information, see Government employees outside Canada
Your residency status if you entered Canada
If you left another country to settle in Canada and you established significant residential ties with Canada becoming a resident of Canada in the tax year, you may be considered an immigrant
If you have residential ties in a country that Canada has a tax treaty with and you are considered to be a resident of that country, but you are also a factual resident of Canada because you established significant residential ties with Canada, you may be considered a deemed non-resident of Canada. The same rules apply to deemed non-residents as non-residents of Canada