Chapter four, verses 13-18, speaks to this. Easter, however, celebrates a bodily resurrection. For that we must wait until the general judgment when body and soul will be reunited in heaven or in hell. For people living at the end of the world, the particular and the general judgment will be the same event. For everyone else, these will be separate events.
Purgatory ends with the last judgment.
I encourage you to continue to pray for your sister. No honest prayer is ever wasted. The Wise Man welcomes your questions. Include your street address for personal replies, please. Some answer material must be mailed since it is not available in digital form.