Has to be her principal residence to avoid capital gains.
http://www.cra-arc.gc.ca/E/pub/tp/it...it120r6-e.html
In order for a property to qualify for designation as the taxpayer's principal residence, he or she must own the property. Joint ownership with another person qualifies for this purpose.
The housing unit representing the taxpayer's principal residence generally must be inhabited by the taxpayer or by his or her spouse or common-law partner, former spouse or common-law partner, or child.
A taxpayer can designate only one property as his or her principal residence for a particular taxation year. Furthermore, for a taxation year that is after the 1981 year, only one property per family unit can be designated as a principal residence.