Meaning of 'put in a little apartment'

[Daddy]

Gloria: My mother-in-law is always criticizing me. She doesn't like my cooking, or the way I take care of the children. What advice do you have for me?

Dr. Burk: Gloria, I have a couple of ideas, but first, how big is your house?

Gloria: We're lucky. It's quite big.

Dr. Burk: well then, here's a suggestion. You could put in a little apartment for your mother-in-law. You just need a small kitchen, bathroom, and a bedroom.

Could you tell me what put in a little apartment means, please?

Thanks.

Daddy

[Mister Micawber]

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Put in = install.

Put in a little apartment = construct small and separate living quarters within the larger house; build a little apartment within or attached to the house.
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Native English teacher at Mister Micawber's