My DeLorme inReach can send a message with coordinates and then doesn't need to remain online and continue transmitting. (Of course, you want to keep it online so you can continue to communicate with SAR, but if the battery were to die they would still find you as long as you don't move from your transmitted location in your emergency call.) So a solar charger, etc. wouldn't even really be necessary, and it will stay online for quite a long time between recharges.
Many long distance backpackers will carry high capacity USB battery packs to recharge devices off rather than a solar charger, as they weigh less and involve less hassle and can generally last between town stops every 5 to 10 days (depending on what trail, of course).
I'm not familiar with all PLBs/satellite communicators but my inReach works internationally.
That does seem a possibility—or once she set up her camp she remembered the somewhat poor advice of staying put (this can be good if you're actively being searched for and likely to be found quickly, but once days or weeks have gone by can be bad to continue as your chances of being found decrease).
There are a lot of good ways to leave "telltales" you can follow once you're in a situation where you're lost. Branches forming an arrow on the ground back towards your camp, each within sight of the next, are an easy way to do it.
I'm not aware of a similar thing in the US. And depending on the remoteness of your location, you may get an indication of a good signal (3+ bars) but still be unable to transmit or receive a text. It's common in the mountains where I hike and backpack to get "ghost bars" like that which suggest you should be able to send and receive messages but only a tiny percentage ever get through, if any.
It's not dangerous if you have navigational skills. Most people, however, do not, or haven't developed theirs very effectively. I see it myself sometimes with other hikers at the front of a group—they take a wrong turn and suddenly have no idea where they are and start freaking out rather than just backtracking. Fortunately they're in a group, generally of people who can navigate and do know where they are, but when someone with poor navigational skills gets into that situation it usually leads to panic and bad decisions.
It's not at all extraordinary that a hiker of her age decided to go backpacking alone (which in this case she didn't—she was with someone else who left). It's a very common thing for people to solo hike and backpack. Carrying a small amount of gear is not a problem either—it's the norm. But navigational tools of some sort, even just a micro compass and a map, are generally considered an essential.
Please don't do this. I see people doing it, even going so far as to leave flagging tape on obvious, maintained trails so they don't "lose their way". And usually people don't remove it after. It makes an area trashy, especially when done unnecessarily—and saying you should do it whenever you go off-trail is very unnecessary.
If your navigational skills are poor enough that you can't trust yourself to walk off-trail without getting lost, use a passive system like running a GPS receiver during your hike so you can backtrack along its track until you find your trail.
They're growing in popularity, but they're expensive and some of the popular ones (not PLBs specifically, but satellite trackers & communicators) like SPOT and DeLorme inReach have monthly subscription fees as well. Someone who isn't out alone all the time may not feel they can justify the cost.
I carry an inReach and find it fantastic. I've never used it for an emergency (though an emergency leading to a late-night Air Force helicopter rescue of someone in my hiking group several years ago prompted me to purchase it) but it's fantastically useful for text communication with friends and family in areas with zero cell reception, as well as (very recently added) weather forecast downloads for your precise location. And in the event of an emergency, being able to communicate details about your situation is very useful sometimes.
I'm a very regular hiker and backpacker, and while I always feel bad in situations like this, I also always feel that people who get lost so easily that they can't find the trail—especially one so developed as the Appalachian Trail—after stepping off it for a few minutes shouldn't be hiking alone, or should be using some sort of navigational aid to help avoid that happening. She wasn't initially hiking alone, but she should've left when her hiking partner did if she wasn't competent enough to navigate solo.
Perhaps I'm unusual among hikers, in that I hike off-trail regularly, hunt for lost and abandoned trails for fun, and am a trailwork volunteer with the Forest Service, but I cannot understand how people get lost. If you lose the trail, you simply go back the way you came until you find it again. And yet people get lost all the time.
Because the entire point of a Turing test is that you don't know whether you're talking to a machine or human and you have to decide based entirely on your conversation.
The Real Name policy was the beginning of the end for me, Reader being shut down made me lose interest in all new Google products, and Snowden made me stop using some of the ones I already had been.
Many long distance backpackers will carry high capacity USB battery packs to recharge devices off rather than a solar charger, as they weigh less and involve less hassle and can generally last between town stops every 5 to 10 days (depending on what trail, of course).
I'm not familiar with all PLBs/satellite communicators but my inReach works internationally.