Orbit Law, PLLC | Kripa Upadhyay
In short, Yes, the U.S Citizen sister can sponsor your family member IF the I-130 that the deceased sister applied for has already been approved. The _FAMILY SPONSOR IMMIGRATION ACT OF 2002_ that was signed into law on March 13, 2002, allows you parent, sibling or child who is at least 18 years of age to become a substitute sponsor if a family-based visa petitioner dies following the approval of the I-130 petition but before you obtains Lawful Permanent Residence ("Green Card"). Unfortunately, there is no provision for a substitute sponsor if the I-130 is not approved prior to the original sponsoring relative's death.
Answer Applies to: Washington
Law Office of Immigration & International Trade Law | Linda Liang
The old petition is still valid, i.e, you don't need to change anything. You need to retain a lawyer to help you.
Answer Applies to: Florida