You clearly didn't understand the plot--but there was one. If you rewatch, you'll see that after touching the candle, Mirablel wipes her hands on her dress before touching the door. She didn't get a door because she transferred the candle's power to herself, becoming the new candle. That's what she was able to bring the house back after the candle went out. Unlike her cousins, whose powers are tied to their door/room, she alone had the power within her.

Another thing you may have missed is the fact that this is a deeply cultural story about generational trauma. What makes Mirabel special is that, by not having "overt" powers, she gains outside perspective. "Mira" means "to look" in Spanish. She breaks the cycle of trauma by seeing and confronting the problems faced by the family, caused by the trauma of losing Abuelo. The Colombian cultural elements are very important to this story, and dismissing them as "shoehorned diversity" or whatever is really gross, FYI. The Latine community comes in all shapes and colours, and the film does a really good job of showing that, as well as incorporating real history and trauma without "kiddifying" it.