Is the mother of a divorced wife considered one of the Mahrams, and is it permissible to shake her hand and sit with her?

A woman is forbidden to a man if she is among the women forbidden by lineage (mothers, daughters, sisters, paternal aunts, maternal aunts, nieces from a brother, nieces from a sister), or forbidden by suckling, or forbidden by affinity (father's wife, son's wife, wife's mother, wife's daughters). The wife's mother is forbidden to a man as soon as the marriage contract with her daughter is concluded, whether he has consummated the marriage with her or not, and whether he divorces her or she dies. This prohibition also includes the wife's mother through suckling. It is permissible for a man to show her what he shows to his mahrams, and to shake her hand and travel with her, unless there is a lustful gaze or fear of fitna. However, before the legal marriage contract, the fiancée's mother is a stranger to him.