Here's a way:
Take VIA from Ottawa to Toronto's Union Station, then take either the Milton GO train from Union to the Cooksville station in Mississauga (afternoon rush-hour service weekdays only, outbound from Union) then a cab, or the GO bus from Union Station (cross Bay St. to get the GO bus) to Square One, where she can take a local bus or cab to Heartland.
Or take the Lakeshore GO train to Port Credit, then Mississauga Transit to Square One, to transfer to a Heartland bus. Fare on Miss.Transit is only 50c if you show your GO ticket when boarding.
bj-21.