@lentinant already mentioned one of the reasons why Nesuko is stronger than other demons because she is able to survive after taking a lot of blood from Muzan Kibutsuji.
Muzan Kibutsuji may be tried to kill by exploding her after injecting a lot of his blood into her veins but maybe somehow she able to survive with that much of the blood that makes her powerful demon.
One of the episode we say Muzan Kibutsuji frighten of Nesuko father when he found the same ring and scar on the face of Tanjiro
apart from that, I will say her father was a demon slayer too maybe he was researching to protect human from becoming a demon. he able to create a vaccine with which a human can control his will after becoming a demon too. he injected his family with the vaccine because he knew Muzan Kibutsuji will come after him & his family in future. there may be some limitations on a vaccine like it should be injected before becoming a demon.