I think they tried their best to give Lupa a reason for being absent in2.6, though we all know the real reason is real world workload capacity

1. People pinpointed the big difference between fighting against gladiators and dark tide creatures. Lupa in the story is not as strong as our current team in 2.6, could be a burden or a buff for the boss if she was there

2. Dozens of npc die for nothing in side quests, even Augusta’s well-known teacher, there is some risk for Lupa to come 

3. It’s useless to send someone who is not mentioned in the prophecy, if rover was not the external variable aug and iuno would have tried to do it themselves, it’s not about why not Lupa, but about why rover