Pretty sure it is the idea that she was our first ally in the game and guided us among many parts of the game. Then, on second dream even after going against her wishes and flat out ignoring her. She came, in person, for the first time. To help you.
Not that we can fault her, she is after all the reason we, the tenno, went on a genocide against the orikin.
Now. Some lore. As we all know. The "Orikin", the creators also know as the ones to have made the tenno. Are the human race. It ties in a similar way to the plot of Halo.
Anyway, The Orikin. The pinacle of humanity, we created the Grineer, Infected, and Sentients. The corpus are just the remains of our race. Which have become more akin to dog breeds in which the credits and commerce are what makes the breed higher.
Grineer, clones made to get easy organ replacement and slaves. The Sentients, terraforming machines. The Infected were created to fight The Sentients after they rebelled.
After the sentients rebelled against the Orikin. They created the infested. The infested didn't work as planned, but they were close. So, they created the Tenno. Fusing both the power of the infestation in armors, and young humans. They made, the first Tenno. "Machines" to fight the sentient Hunhow or something. Too bad, the Orikin saw the Tenno as too powerful, and wanted to end them. Too bad for them, that "Marculis", also know as Lotus. The only mix of a Oriking with Sentient powers, the "daughter" of Hunhow. Took pity on us, and wanted to help us. It was because of her, that we Tenno rebelled against the Orikin. We brough them to extintion. Then... we went asleep. But the Lotus, as always. Just wanted us to "live". Knowing our past was not really something that we needed. So she was against the idea of us confronting the past. Because, for all intenses and purposes. Lotus send us on a path to end the Orikin. We almost succes, some remain. But the golden days have been left behind. They are no better than Grineer clones. Corpus is what we call them now.
That is what I got from the forum and the Wiki. It's higly hypotetised that Ballas did something to Lotus to change her mind. Some say he woke up the "sentient" inside of her. Which would explain what happen to Ballas and why she wants to, well. Terraform the solar system and end every other race? For all we know it is Hunhow's dead man switch that ballas activated inside of lotus.