I am saddened by this tragic loss of your daughter. RSV infection of the lungs typically causes inflammation of the bronchial tubes of varying sizes; much less often it may cause pneumonia, especially with diseases of the immune system. When that occurs it would be apparent on both chest X-ray and at autopsy. Were RSV bronchiolitis to have been the cause of death, that should have been evident at autopsy, even if the RSV was not isolated and identified. That neither was the case makes it highly likely that your daughter did not die of RSV infection of the lungs.
With RVS infection of the central nervous system, involvement of the center that controls breathing might have been a factor. The tone of your message suggests to me that it might be important to your emotional well-being to know, with reasonable certainty, the cause(s) of your daughter’s death. For that reason, I strongly suggest that you schedule a time to meet with her doctor, in his/her office to discuss these issues and get answers to your questions.
Again, I feel bad about your loss.