Despite her size and physical maturity, Brittany looks like a scared little girl in that walmart photo.
I think she 'fell in love' with JE.....and that he was a welcome release for her, after her beloved brother passed away unexpectedly. Despite TS's love for her daughter, she clearly feels empty and lost without her son. I could see Brittany wanting to escape that. I've got to wonder if she knows/knew her mother was dead when she was caught on that walmart camera. She looks worried, anxious. I wonder if that's just about running away or if she knows something. It's possible---if they are camping--that she doesn't know about her mother's murder. It's also possible that she participated.
I think isolating her in the woods somewhere is even more dangerous for her. She's 12. She will eventually want to go home, go shopping, go be with her friends, etc.
The temps are REALLY cold down south. It's near freezing an hour south of NC with 14 mph wind gusts. I LIKE camping and I wouldn't want to do it in this weather. I can't imagine a 12 year old girl would either.