The Rogue had apparently changed strategy after noticing her back attacks failing twice. Jack had to give the girl some credit. Her quickness in switching methods from a failed one to a successful one was indeed impressive.
Maybe she thought the reason her opponent had managed to evade her backstabs was that he was on guard against back attacks, and she was not far off with that deduction. If that was the case, then she just changed to attack from the side, while masking her attacks behind those other players. Taking a slice here and there in between the small windows of opportunity.
Jack was dismayed. It was easier to notice the back attack on his radar because only the Rogue had the speed to catch up to him from the back. But if it was from the side, it was more difficult for Jack to determine which of the multiple red dots were the Rogue. Hence the Rogue had managed to land several opportunistic blows on him without him noticing.