Ruth got money from her husband (Macon Dead) to give Hagar a decent and respectable funeral. After Hagar died Pilate and Reba had little money for the funeral and burial since they gave most of their money to Hagar for makeup and clothing to make herself feel accepted and loved by Milkman. Ruth demanded that Macon give her money, and she wouldn't leave his office until he gave her a satisfactory amount.
Ruth was perhaps reciprocating Pilate's kind acts toward her. It was Pilate who gave Ruth the concoction to seduce her husband, which led to Milkman's conception. Pilate also saved Milkman from Macon's attempts to abort him by scaring him with a voodoo doll.