Your mom doesn’t have ties to return. It is a job, income property etc. Volunteering is not a tie to return. Maybe try one parent only applying so tie to return is the spouse.
There have been a couple of such cases on this forum where parents' visa has been rejected. Like already mentioned above there is the risk of overstaying after the delivery. I would also recommend a 2-3 week itinerary max and about 10-15 CAD for this visit.