If someone talks you through something that you do not know, they explain it to you carefully. Now she must talk her sister through the process a step at a time
If you talk something through with someone, you discuss it with them thoroughly. He and I have talked through this whole tricky problem Now her children are grown-up and she has talked through with them what happened It had all seemed so simple when they'd talked it through, so logical He had talked it through with Judith