Unfortunately without an autopsy and a body to exhume, Jessica's family will need to rely on witnesses to tell the truth about what happened to Jessica.
Because she was sitting on her feet, she would not be able to lean back, her backside would be elevated, she will die in that position.
If there were not any indications that she walked bare foot for some time then again you have to go with this is a suspicious death and there for an investigation is necessary.
I hope that helped someone learn something new.