Delays in getting the brass plates

I never thought about it before but Sariah might have only begun to complain to Lehi after her sons should have been home from their trip to Jerusalem. The fact that their first two attempts failed means that they were at least one day later than she would have expected (assuming that the first two attempts were both made on the same day). If they feared that Laban would kill them Sariah may well have thought the same thing so when they were at least a day late returning she thought they were dead.