My mom came to Canada as a visitor with multiple entry visitor visa in March 2018, this is her third time visiting us, CBSA officers entered a stamp when she entered in March 2018. After 2-3 months, she went to visit my sister in USA but she had to stay there for 2 months due to some family reasons and while she returned to Canada in August 2018, they didn't' affix any stamp at the airport, so that means, she can still stay in Canada for 6 months from August 2018 or she has to leave after 6 months from first entry in March 2018. Kindly advice ?