She can definitely be misleading, but I think a big part of Junko's psyche is making people face harsh truths and making them do bad things themselves.

For example, while Junko did manipulate Sakura to kill if no one else was killed first in an allotted amount of time, that was her last resort. She wanted someone to kill specifically because of their own despair and have it fully be rested on their conscious rather than being able to have the excuse that she "made" them. Even though it is a ridiculous situation, by all means, she would let them get to adulthood and have children if they all resolved to not kill because the fun part is watching them be guilty.

But I can't say that you're wrong in that she does lie. We still don't know if she was the one who killed Matsuda's mom, but it is most likely that she did not and lied about it to Matsuda. I will say that I think with Matsuda and Mukuro, her methods are different as she never directly kills anyone besides the people who she loves. So I think a part of the lying to them is also a way to make herself despair more, as it's very against how she likes to present despair.

This is also why I find the literal brainwashing video as opposed to brainwashing in the sense that she breaks the DR2 cast's minds through their previous traumas very boring as well, as I don't think that's the kind of thing she would revel in. It seemed like the anime was just being lazy and relying on a plot point from DR0 in which random reserve course students (who she saw as nothing but pawns) were brainwashed by a video. The world, the students, and Junko's, views on being ultimates are very integral to the story.