Because you are only connected through marriage and not by blood, your cousin’s wife is your cousin-in-law. The suffix “-in-law” can be used to express your relationship with the spouse of any of your blood relatives.
The suffix “-in-law” is only for persons who marry your relatives, not their family. Although your cousin’s wife is referred to as your cousin-in-law, there is no universal title for your cousin-in-mother. law’s Depending on the circumstances, it is easiest to use names or descriptions for these people. To someone who knows your cousin’s wife, you could use “Helen’s mother,” or “my cousin’s wife’s mother” to describe the link to a stranger.