Haha, first of all, do you get alone with your mother-in-law.
Well if you both are only in good terms, I would say to do the same as to what you would do to any mother, you can do the cooking breakfast thing OR pretend you dont remember and cook her dinner instead. Gather up her whole family like her kids and husband and yes your family too.

If you are in bad terms at the moment or always had been. Here is my tip since i have done the same last year. I wanted to show her I was a good match for her son and nothing to prove that I was willing to crawl for her. I decided to take her to my parents home and show that I help my mom prepare things then I took her out to the beach, since we are in Hawaii and she WAS a filipino immigrant and very old fashion, my parents and the rest of the clan took her to bellows beach HAHA. and i thought it would blast her off but only thing she had a blast lol.

or you can simply just tell her you want to spend the day with her. like shopping etc. and it's better than moping around to think of what to GET her.

I personally when buying a gift would give something from the heart. You don't have to spend lot's of money or buy chocolates etc, but show your mother in law that you care for her also by giving something create and rememberable. The best gifts are the ones that you had something to do with and not always the ones that cost alot, so try and find, make, give a gift that will mean something special to your mother in law! Hope this helps!

Handwritten card:

outside

Dear Mother-in-law,

inside

You don't have to pay for your insufferable daughter any more.

Happy Mother's Day.

You owe me.

Love,
Your Son-in-law

You can gift to your Mother-in-law as per her choice means what she likes the most jewelry, handbag, home decor or also present her God idols. Add a flowers bunch and some yummy chocolates for her. That will be the best Mothers day gifts to her.