I would keep her in a cage. Feed her twice each day. Ensure she has fresh water to drink, and I would fit a little run wheel in her cage so that she could exercise frequently.
I wonder what 12" ladies eat - Sunflower seeds?
Fortunately, there are also 12" gentlemen listed on the group. Perhaps if a 12" gentleman met with a 12" lady, their mutual search would be over, and they could live happily ever after in their cage.
I would carry my 12" pet lady in my pocket. Friends would praise my compassion for keeping and caring for a 12" lady and might even want one for themselves.
Alternatively, it might be possible to set up a website for 12" people. They would be able to socialise, meet in person, though mail carriers would need to take care transporting the little boxes the 12" people travel in.
Buying new clothes for my 12" pet lady would be simple. A visit to Toys R Us would quickly resolve the matter of finding 12" clothing, also toys for them to play with. Perhaps a Barbie or Ken doll for them to acquaint with.
Yes, owning little people could be fun. One could dress them in toy armour and have them re-enact battles from the English Civil War or, indeed, clothe them in Elizabethan garb and train them to perform Shakespeare's "Comedy of errors", but certainly not "Much ado about nothing". The 12" pet person might take that personally.
What an amazing idea I have had. Join the 50 plus club and adopt your own 12" pet person!