Mary's has a gentler slope than others in this area, and the ridges which connect it to these other peaks, as well as the number of trails on it, make it easy to come up one way and descend another.
With several approaches possible, your best bet it to follow the trail up Judi's Peak and continue on the high north ridge, hitting Mary's summit in just a quarter of a mile.
Map & Directions
From Seattle take I-90 East to Exit 85, turning right onto SR-970. Go 5 miles and turn left onto the Teanaway River Road. Follow signs for the North Fork Teanaway about 13 miles to a junction at 29 Pines Campground. Take the right fork, going 3 more miles to the junction with the Beverly Creek Road. Turn right onto this road, and follow it 1.5 miles to the road end and trailhead for Beverly Creek Trail.