Umm Salama
When Fatimah bint Asad (mother of the 4th Caliph Ali) died, Muhammad is said to have chosen Umm Salama as the guardian of Fatimah bint Muhammad. However, the latter Fatimah is thought to have married Ali in 1 AH or 2 AH, Fatimah bint Asad died in 4 AH, and Umm Salama married the Prophet in year 5, so any guardianship must have been purely nominal.