Steven Universe - I love you Lapis, but even I know this is the truth...

I was doing just fine when I got you of that mirror, but then Jasper and Homeworld just HAD to show up and get on my last nerve.

Things ARE getting better, though.

Her personality is easy to understand: She's traumatised by everything that's happened to her after visiting Earth, but after being abused by Jasper, she snaps and decides to control somebody else's destiny by becoming Malachite with her, not knowing she's unleashed the most dangerous threat this world has ever seen, even stronger than Alexandrite, but thankfully, the Crystal Gems free her. Unable to go back to Homeworld as she was just shipped back to Earth anyway (If Peridot and Jasper didn't find her on the way to Earth) she decides to crash at Earth and slowly adjusts to the way of life there. She comes off as happy when expressing herself with "art" or being around Steven, comes off as moody when doing stuff she doesn't like or being around people she doesn't like, scared when tackling the unknown.

tl;dr she's recovering from trauma and is slowly becoming a normal person.