She was played by Amanda Brooks.
Rebecca was shown as one of the many Army wives in a support group conducted by Dr. Donna Sue Monaghan. However, Rebecca was also the lone female in a triumvirate who robbed a warehouse that carried anti-depressants. The group was led by Mark Van Zandt and also consisted of Greg Collette, who participated due to his wife, Brandi (an Army vet), committing suicide due to being denied medication for her PTSD. During the armed robbery, Rebecca and Greg donned ski masks, and the former shot security guard Lee McKinnon (non-fatally). In the meeting, Rebecca spoke about how Gareth was getting better due to the medication.
The trio committed another robbery in the episode's climax, with Mark and a masked Greg holding a truck driver at gunpoint. Longmire captured Mark and unmasked Greg, but after figuring that they had help in the last robbery, Rebecca appeared in her villainous masked disguise and pointed a gun at Longmire, marking her reveal. Mark and Greg attempted to persuade Rebecca (without referring to her by name) to put down her gun, stating that Longmire doesn't know her identity so nothing will happen to her. Despite this, the villainess removed her mask and ordered Longmire to get down on his knees.
Longmire made his own attempt to keep Rebecca from crossing the line and resorting to murder, but Rebecca remained adamant, stating that Eli needs a father (a reason for her quest). Longmire stated that Eli also needs a mother, and compared Rebecca's actions to the end of Of Mice and Men (George killing Lennie to prevent him from being lynched), calling what she was doing an act of love. An emotional Rebecca finally put down her gun and later broke down in tears, right before she was arrested (off-screen).