Is there any idiomatic synonym for "to apply a double standard"? [closed]

Solution 1:

The mother is "playing favorites" in giving her daughter preferential treatment.

http://www.oxforddictionaries.com/us/definition/american_english/play-favorites

Solution 2:

Answer to edited question:(to show the syntax)

The mother applies a double standard in dealing with her daughter and her daughter-in-law.

The mother employs a double standard in terms of how she treats her daughter and her daughter-in-law.

Solution 3:

This mother has a policy of one sauce for the goose and another for the gander

What's sauce for the goose is sauce for the gander

Prov. What is good for one person is good for another. Jane: You're overweight; you should get more exercise. Alan: But I don't really have time to exercise. Jane: When I was overweight, you told me to exercise; what's sauce for the goose is sauce for the gander.

McGraw-Hill Dictionary of American Idioms and Phrasal Verbs

This mother is giving her daughter in law the short end of the stick

If someone gets the short end of the stick, they are unfairly treated or don't get what they deserve.

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