I’m sticking with you, Joanna.
On finding flaws, I didn’t have to look too hard. Your story is all about cheating the system and lying, right? I just moved past the soft language. It may be hard to do that if you are in love with the character. It may feel like saying your baby is ugly. Yet you had the essential ideas about her in the first description of your story.
If your CPs are bedazzled by her, they won’t be much help. They may even excuse/defend her. (Think of how Star Wars fans say Han did not shoot first. Against all evidence.)
You might find someone who doesn’t like Justyna who can easily point to (and emote about) her flaws. Would you listen that person? Trust their judgment? Would it be helpful.
I think if you want a big character arc for this story, you’ll need to find it within yourself. Finding flaws and torturing protagonists are the hardest parts of working on a story with a character you care about. Most writers cannot do these things, which is why most stories don’t stand out.
But hope comes from practice. Either by playing with a new story of yours or with someone else’s story. The door to more powerful stories may not open right away. It may mean writing a lot of pages not meant for publication.