Bri was a very good witness in that she was consistent in her testimony, she repeated what was said to her in that call, she admitted her own anger at Heather even picking up the phone when that mystery call came in.
As far as Heather not being truthful... how does it change the fact that a crime occurred?
Heather was allegedly upset and crying and she was apparently not expecting to hear from SM. So if SM says something (anything) to encourage or persuade her to come out that early morning and she is led into a trap of some kind (even if he didn't personally plan the trap itself), he's still guilty under the law. Not believing the victim is a little bit of victim-blaming by jurors, IMO. But even if one is convinced there's more to the story than what Heather told Bri, how does that change what happened to Heather into not being a crime?
Did Heather consent to being 'disappeared?' Did Heather consent to being removed from wherever it occurred and consent to being kept from getting back to her car and back to her apartment? If no then a crime occurred.
The trajectory of Heather's car & cell phone and SM's truck both heading to PTL around the same time doesn't change. Heather being disappeared (harmed) doesn't change. None of it makes SM innocent if SM participated in or allowed harm to come to Heather that early morning. Thus a juror's opinion about Heather's truthfulness is irrelevant because the end result doesn't change.