My theory is her father was angrier about the first car accident than he lets on in the interview. This probably aggravated Maura's already fragile emotional state (perhaps depression).
She was not in a good frame of mind, decided to take time off and drive to where she is comfortable (Vermont or the White Mountains). She emails her professor that she had a death in the family and needs to be gone a week, which was untrue.
She drives North, buys some alcohol, and drinks while she drives. It turns night. She is driving along a dark New Hampshire road and is impaired. She hits a very sharp left turn and reacts too slowly, wrecking the car in a snowbank.
This is her second car wreck in days. Now she is shattered. Plus, she is intoxicated. She has no idea what to do. She can't call the authorities because she would be arrested for a DUI. She can't call her father because he is too far away. Moreover, there is no cell service. She stands outside the car trying to make sense of her situation.
The bus driver stops, asks her if she needs help. She declines (because she doesn't want him to see she's been drinking),and says she called AAA and they are on their way. The bus driver suspects this is a lie because there is no cell service.
What happens next is more of a mystery. I suspect she panicked, thinking when the driver got home he would call the police. She didn't want the cops to find her inebriated by her disabled vehicle, so she takes off on foot, even though she has nowhere to go.
She treks into the woods to hide, her head not straight because of her emotional troubles and her intoxication. Only problem is it is a very cold night in New Hampshire and the woods are thick. She either got lost or simply remained in one spot too long and died of exposure. I know that search teams have combed the woods, but we are talking about a huge area of thick woods. In cases past, it's not uncommon for searchers repeatedly to miss a body 10 yards away under such conditions. Afterwards, her remains likely were eaten by animals, further hampering any attempt at location.
Likely, we'll never know for sure what happened to that poor girl. Maybe one day a hiker in the woods will come across some evidence that will put everything in a better perspective.
WRT the phone call...
By that time she would have been exposed to the elements for an entire night, and it's likely she was suffering from hypothermia. She had spent hours wandering deep enough into an area that finally had cell service. When she makes the desperate call, all she gets is his voice mail. In her condition, it's doubtful she could even speak at that point. If that was her message (which unfortunately cannot be proven), I think she died shortly thereafter.
Possible. Although, I don't think she was intoxicated enough to have been driving drunk, but perhaps, she wasn't sure, because she knew she was drinking. I do think she wasn't looking forward in telling her dad that she was in NH and her car was wrecked, especially after wrecking his car a few nights prior. There is no doubt, she was in a dilemma. I do think she walked away from the accident, but how far she ran off is a mystery. I have 3 theories: she succumbed to the elements, accepted a ride from a bad person or she was hit by a vehicle which threw her into the woods. My last theory is probably less likely, but possible. A fast moving vehicle or a truck may have thought they hit an animal or they just plain drove on to avoid responsibility.