Per her boyfriend, she didn't pack a stove on this trip because of the weight. She did her food shopping the day before heading to the trail (via security camera footage) but they don't know what she took.1. The skimpy plan. LM was supposed to be hiking for 3 days. She had a history of hiking the Long Trail in VT. Overnight hikers on major trails like the LT and AT have veritable cult commitments to travel light. Unclear how LM might fit in that scheme. She might have just decided "one day in, one full day on the trail, one day out, let me see, I'll take 2 dinners, 2 breakfasts and a bunch of snacks, but not too many. I can fill up when I'm done." I have a feeling (feeling only) this is probable (I have encountered ALOT of LT hikers), and this would be the MAX they take. This method also counts on others to provide for you if you've screwed up your plans, and it's very problematic if there's no one else around.
2. Traditional planning, standard rule of thumb. I did most of my hiking learning in the PNW with a club like the Mountaineers, but have also done ultra-distance thru hiking. I carried more than most thru hikers, but about standard for a backpack trip, e.g. in the PNW. You take an ENTIRE extra day of food, and you take extra energy bars, just in case. On a trip like LM's to the EV, I would be taking 3 days of food at 2lbs per day and my spare day maybe on the light side (7.3 lbs total).
But here's another dimension of the problem. There is generally some kind of cooking involved. These days, you pour boiling water on your prepared food, and it sets up. No need to actually cook. However, you'd be carrying a stove and fuel. There is a second advantage to this: if it gets cold, you can heat yourself some water to drink. (Hot Jello is standard SAR fare.) But if you're in a deluge......I'm not sure how this would work.... It would be very complicated if your safety required you to stay in your tent. Under no conditions can you safely use a stove in a tent (carbon monoxide poisoning) or even the vestibule.
Which brings to mind..... if LM had a stove, she'd have been able to start a smoky fire. Many stoves have piezo's (like a Bic lighter) or a spark, so don't require matches: no issue with wet matches. She'd have had to find something to burn, but IMO there should have been a smoky fire in this case, and for sure it would be spotted (e.g. from the air). It's possible she didn't take a stove (per ultralight thinking), but I think more likely hypothermia happened very early in the trip.
Pro tip. I've provided this before, but I'll do it again! Get some cotton balls and smear vaseline on them. Put them in a baggie in your (day) pack along with a lighter. They take up almost no space. They are fire starter. Alternatively, take trick birthday candles (they don't blow out). You will use these to start a smoky fire if you need help....