高手帮忙解释一下啊！！My daughter smokes. While she is doing her homewo

高手帮忙解释一下啊！！
My daughter smokes. While she is doing her homework, her feet on the bench in front of her and her calculator clicking out answers to her geometry problems, I am looking at the half-empty package of Camels tossed carelessly close at hand. I pick them up, take them into the kitchen, where the light is better, and study them -- they are filtered, for which I am grateful. My heart feels terrible. I want to weep. In fact, I do weep a little, standing there by the stove holding one of the instruments, so white, so precisely rolled, that could cause my daughter's death. When she smoked Marlboros and Players I hardened myself against feeling so bad; nobody I knew ever smoked these brands.
She doesn't know this, but it was Camels that my father, her grandfather, smoked. But before he smoked cigarettes made by manufacturers -- when he was very young and very poor, with glowing eyes -- he smoked Prince Albert tobacco in cigarettes he rolled himself. I remember the bright-red tobacco tin, with a picture of Queen Victoria's partner, Prince Albert, dressed in a black dress coat and carrying a cane.
其中She doesn't know this的this指的是什么？？？