What does it take to have a Granny Pod installed at my home for my mother?

Based on your description of your mother on your other thread , your mother is not able to live in a granny pod by herself . That ship has sailed .
She needs 24h supervision now .
Her dementia will only get worse . It’s too late to spend money on a granny pod. Save that money for memory care .
Also read and learn more about Dementia .
I don’t recommend having Mom move in with you unless you also have hired help coming in to give you breaks. Again , Mom can not be left alone , nor can she drive .

A granny living in your back yard could soon be your worst nightmare. Once she's housed there, you're on the hook to become a full-time caregiver. Look up the job description before you commit to the job! BTW, I am one now and have been family caregiver in the past as well. The work is hard and the perks are few! Read and heed.

Only do this if you are willing and able to become her FT caregiver. Even if she has all her faculties now, she will slowly lose them, and maybe even become uncooperative, wander off at night, become fecal incontinent, etc.

Will adding a pod make your property less attractive to future buyers? Who is going to pay for the pod and the costs of insurance, taxes, maintenance and upkeep?

Maybe it's better to just find a great continuum of care community that starts with IL and includes, AL, MC, LTC and hospice and have her save her money for that instead of locking it up in real estate?

If you are in an HOA, please check the rules. I was going to build a place for my parents, but the HOA, said NOPE.

For the granny pod to be habitable, it will almost certainly need a water and sewer connection, plus power. Those are likely to be the expensive tricky bits. Check first if it is allowed!

You'll need to go online at your city or county website to see whether they are allowed and if so, what are the requirements/limitations. Then you can start looking for the options available.