* First, forget about making excuses. You need to agree with her that you screwed up big-time, and you need to admit it. Sincerely, contritely, loudly and often. Sincerely apologise and say sorry.
* Next, get ready to make a gigantic concession of some sort. Maybe, you could consider a vacation with your in laws that you have been avoiding for quite a while or do something that she has been asking you to do.
* Take her out shopping, plan on watching a movie together and finally take her for a nice and cosy dinner. Spring a surprise on her, maybe get her some flowers, buy a perfume or something like that without being asked to.
* Take a good look at her and compliment her on how nice she looks in the lovely dress that she is wearing.
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