Not sure where the MIL is flying from but a ticket doesn’t mean that the flight won’t still get cancelled so you also need to prepare for that possibility. Seems lots of people have had multiple flights cancelled since the situation is so fluid. There is so much discretion when it comes down to cases like your MIL. Her reason for travel wouldn’t be considered essential. If living with you you‘ll need to be prepared to quarantine yourselves for 14 days unless she can get home from the airport on her own and can be segregated into part of the house like a basement with her own bathroom. This may not be possible for all families. Does she have health coverage that will cover covid treatment? Depending on the province she may not get free treatment for covid so the potential expense will need to be considered. You’ll have to look up your province. Domestic travel may not be possible. Any older person should really be avoiding travel because the chances of exposure are much higher as people try to return to Canada.. If your MIL has any health issues that would be another risk factor. There are lots of unknowns and lots of things to consider. Currently only one family member is able to enter the hospital with a woman in labour until discharge. Hopefully women will continue to be able to keep one visitor but many hospitals are not allowing any visitors unless you are in the ICU, are a child (you can have 1 visitor with you at all times and only 2 nominated people who can rotate) and L&D who can have one person nominated as their visitor for delivery and postpartum.
Agree that the attempt to fly is a personal choice but if you decide to go ahead with it would suggest you remain guarded until she is actually on the plane.