Final answer:
Mary Warren and the court have accusations made by the girls during the witch trials as hard proof against Sarah Osborne, but these accusations were not supported by concrete evidence or reliable witnesses.
Step-by-step explanation:
The hard proof that Mary Warren and the court have against Sarah Osborne is based on the accusations made by the girls of Salem Village during the witch trials. The girls claimed to have seen Sarah Osborne engaging in witchcraft activities such as riding broomsticks, sitting in trees, and appearing as a wolf. However, it is important to note that these accusations were made during a period of mass hysteria and were not supported by any concrete evidence or reliable witnesses.