There are three main routes to climb Baldy (the Bear Canyon Trail, the Ski Hut Trail, and the route via the Notch & the Devil's Backbone) as well as some more obscure & difficult ones.
Of these three, the Ski Hut Trail, aka the Baldy Bowl Trail, is the middle in terms of difficulty. (In winter, it's also safer than the Devil's Backbone.) The Ski Hut Trail ascends almost 4000 feet to the summit in less than 4 miles. At 8,200 feet, San Antonio Ski Hut is a little over halfway to the top in terms of both elevation and distance.
At the beginning, you're on a fire road; the elevation gain is harder because most of it doesn't start until you get to the Ski Hut Trail, which isn't marked. I think they figured out that LH initially overshot the entrance to the Ski Hut Trail, which is not unusual.
A February 11 review of the trail on AllTrails there mentions how slippery the trail was. So yes, she could've slipped on a rock, or just slipped. If the trail was covered with snow, it's also possible that she got a bit off-trail and
then slipped. I've also heard that there are some confusing spots on that trail, so maybe she took a wrong turn. (I haven't been up it in years and was with a group both times, so I didn't have to figure out the trail.)
One can definitely go up to the Ski Hut and turn around (which may have been her plan), but it's still a challenging trail. That LH got as far as she did under those conditions implies that despite her lack of experience or understanding of the conditions, she was fairly strong. But she may have been exhausted by the time she got to her last known location.
Here's a description from 2011 of a hike to the summit via that route. To clarify & correct my earlier post, just before the Ski Hut, the stream
is level with the trail. (I think a spring that I contributes to the stream has been diverted through the kitchen of the Ski Hut.) But I don't think LH got all the way up to the Ski Hut. Also, the very top part of the stream near the Ski Hut would've been easy to search. If she'd been found there, it would have happened much sooner and they probably would've said she was found near or below the Ski Hut rather than in the "upper San Antonio Creek Falls area."
Descriptive narratives of hikes by Dan Simpson in the San Gabriel Mountains; including photos and links to trusted hike guides on Dan's Hiking Pages
danshikingblog.blogspot.com
P.S. It's called a ski hut, but the actual skiing on Baldy is much further down. The San Antonio Ski Hut is a backcountry hut that is maintained by the Sierra Club.
JMO