During this trip, all of the Demon tier crystals that were gathered were to go to Zero and Agent 4. That was the arrangement that was made beforehand. Although Flora felt like it was unfair and they were being used, Erin asked her what choice did they have?
They were now hiding behind Pure and were planning to use their army for their goal, and at the same time, they were staying with Pure and being fed every day. Because of all of these things, they weren't really in the position to bargain. At the end of the day, she felt like they were getting more out of this deal than the other.
On top of that, Erin felt like she didn't need anything more in the first place, in terms of equipment.
With her Demon tier armour and Demon tier weapon, she was at the strongest she had ever been and defeating Laxmus was proof of that, she could feel it.
