What are the legal limits for the clothing of the husband's mother (mother-in-law) in front of her daughter's husband, and what is the ruling on her uncovering herself before her daughter's husband?

The 'awrah (intimate parts) of the mother-in-law is the same as the 'awrah of other maharim (unmarriageable kin), for she is one of the maharim. Allah Almighty said: ﴿And mothers of your wives﴾ [An-Nisa:23]. If she is semi-naked, then it is obligatory for her daughter's husband to lower his gaze from her.