You're misinterpreting what I said. I never said she went to the past to prevent Rogue going to the past. I said she went to the past to undo the future Rogue created by going to the past, namely the dragon raid.
Assuming 10 000 dragons really attacked the country, future Lucy went a few days back to the past to prevent that from happening and what happened was the result of Rogue going to the past from, as I said, a future way further away. With other words it's impossible for future Lucy to know future Rogue as they never met. This chapter was the first time they did.
When the dragons attacked, Rogue already had been to the past to cause that attack and then Lucy went to the past where Rogue was preparing this attack to avoid that future. So there are three timelines used: the one we are currently in, the one where future Rogue came from and the one where future Lucy came from.
At least that's my theory, currently there are still a lot of things very unclear. Following this theory it explains as why Lucy would know about the dragon attack and it also can easily explain why future Rogue would know about the attack (as it simply might be not a prediction, but the thing he is in fact aiming at) however it's flawed in it that it doesn't explain how future Rogue would have known how the Games would have ended, which he supposedly started himself as they were meant to fuel the Eclipse gate. It's still not certain either whether he is good or bad, though he definitely doesn't feel good.
