Revision tells us that your sister had a primary or index (first) hip replacement procedure already. Revision suggests the need to remove and/or replace one or all of the implant parts.
The most common reason for implant revision is loosening of the stem on the femoral (thigh bone) or acetabular (cup or socket) side. This can occur with or without infection. The surgeon removes the old implant and replaces it with a new one.
In the case of implants with a polyethylene (plastic) liner, excessive wear can cause tiny flecks of the liner to slough off and enter into the joint. Sometimes the bone around the liner starts to disintegrate.
If the whole implant is removed and exchanged or replaced, it’s like having the surgery all over again. Your sister will have to go through a shortened version of the original rehab program. Having had the surgery already one time, she will be more prepared for the postoperative recovery than she was the first time.
She will be able to tell you if she needs extra help for a day or two. There’s always the chance that complications will occur, which could mean a longer recovery time and the need for more help.