There is no right or wrong here.
She is following her needs, and her needs may not be what others need.
Such is life.
Maybe your mother doesn't have enough internal emotional skill TO handle her emotional reactions to her daughter-in-law, in which case it would case your mom discomfort or even pain to see her. You cannot judge your mother.
Although certainly her behavior is not particularly well-adjusted. But then few us ARE wlll-adjusted. We are all struggling to try to be happy, and some of us understanding where happiness comes from, and others keep trying the same unsuccessful tactics without learning that it isn't working.
But we are all the same .. .restless discontent, trying to find peace from it. Many settle for distraction instead, and all addictions are merely distraction-gone-overboard.