This is unfortunately a common scenario, because gravel shoulders make attractive nesting locations. If you can, watch her from a distance until she completes her nest, then help her across the road IF she attempts to do so. However, the nesting process can take several hours, so this is not always feasible.
In a few parts of Ontario, there are turtle conservation groups that can come watch a nesting female. Check the map at OTCN.ca to see if there’s one near you. Click Nests, click the map pin closest to you, click “View Program Details” and then check the Contact information to reach out directly.