The Sand. No. That is not how heavy sand moves, even if there were motors under it slowly grinding. Not to mention that it makes no sense that is how the defenders of the bridge would stop the Walkers.
The mannerisms. Tara was horrible. Jumpy and twitchy like she thought she was being cool and hip. Cracking jokes while at least 10 guns were on her and trigger happy. This rings false, either these people (at least one of them) would be survivalist enough to just eliminate this threat (not hard, thats what the RULE said to do), or Tara would never have gotten this far in the world not being able to correctly assess a situation.
The sitdown. More lies and jokes. Not realistic. Kill her now. Tara in this situation would not behave this way. Lies are fine, but make them realistic.
Putting myself into Taras shoes would also require me to be able to look into these women's situation. Start with some truth. "I followed a girl here ONE TIME, I could not find this place again." Add options (to killing Tara), "If I were you, Id blindfold me and leave me in the middle of nowhere". Or "keep me chained up here until you can trust me". True Tara looks nothing like the Saviors, but she should at least look like a Survivor. In this episode where we give the real cast a week off, Tara didnt earn any more time alive.