Is my sister's drawing of a girl Haram, given her statement that she is not imitating Allah's creation, and that a tree is a living being that grows and breathes, so there is no difference between it and a human?

The prohibition of drawing images of animate beings is established by prophetic proofs, and the prohibition specifically applies to animate beings, not inanimate ones. Ibn Abbas, may Allah be pleased with him, explicitly stated that trees do not possess a soul, despite being living organisms. This distinguishes them from animate beings, regarding which there is a prohibition against drawing their images and a severe warning for those who do so. Therefore, a Muslim must submit to the rulings of the Sharia and not prioritize intellect over them.