Shizuka's mother, more commonly referred to as Mrs. Minamoto, is a very kind woman. She is very affectionate to Shizuka and her friends. She appears in many episodes in the series. In many episodes, when Nobita comes to Shizuka's house either to show some gadget or call her to his house for homework or to play or else he comes to play and sometimes study at her house, Mrs. Minamoto is often seen telling Nobita that she has gone to the library, or the market, or to her piano/violin class or worst case she is with Dekisugi.

(Source: Doraemon Wiki)