Well if it’s a fake like many say then they knew a lot of info to put it together, email addresses for the contact list, personal pictures (from an airplane taken of Bristol and Trig) that looks like cell phone camera quality....
And since that message is FROM a cell phone then Bristol was in on it unless they spoofed her cell phone number to send the fake email a message from it...or knew what Bristol’s cell phone number is. I highly doubt that Bristol would be in on the faking of Sarah’s personal email address. So that leaves spoofing or knowing what it was.
BTW yea I already left her a message that her number had been leaked onto the internet and she should talk to Dobson/Cellular one to have it changed.