A good quality photo of the affected joint and the crusty area may be helpful.
If it's crust and oozing from infection, then it would need to be addressed.
Leg deformities can happen with any breed of chicken, not just broilers. It's one of those "time will tell" type of things as to whether she can learn to move about on her own and support her weight. Some do o.k. while others don't. She will do better if she's given assistance and daily care making sure she's eating well and drinking.
To cull or not is solely your decision. All of us have different goals, ideas and purposes for keeping chickens.
If you determine that you need to cull her, there are a few ways to cull a tiny chick. For me, up to around 3-4 weeks old, using shears to decapitate is the easiest, quickest and most efficient way. This article gives you info, but it's not graphic and tastefully done.
https://www.backyardchickens.com/ar...-for-squeamish-people-slightly-graphic.74734/