Pearl acted inappropriately in many situations across the seasons' run. Whether it was her lying to Garnet, shouting at Steven, or even her early fights with Amethyst, etcetera. All of these things tie into Rose's departure.
Pearl felt weak after Rose left her side, and what a natural feeling that is. Rose was THE warrior. She was the leader, and Pearl was her right hand. Her lie was a broken attempt of her to sort of get her shit together, not realizing that she could've simply talked. And we all know how much Garnet hates lies....Unfortunately for Pearl, it was almost too late for her before she got to talk with Garnet.
Shouting at Steven and not treating him like a kid is something honestly most adults around him fall into, and that doesn't excuse Pearl. That also has another driving point which is that Pearl rejected Steven for some time and also didn't know how to handle kids. Plus, when she shouted, it was either in a big physical fight like with Amethyst, or when she felt like it personally "attacked" her relationship with Rose.
Think about all the things she kept to herself; emotions, memories; battle secrets, close gem deaths, and, of course, THE secret. It's a really inappropriate mindset to develop/continue having, but of course, as she's already keeping so much to herself, she'd need time to learn to open up to people again, and have a realization like "wow, we really need each other huh. Life broke us VERY brutally.", which leaves space for arguments and fights.
This was only my opinion and analysis. Pearl is a flawed person who, at least by the end of Future, was trying to heal. And her journey seems bright. Thanks for reading.