if i may ask, how old is samantha. reason i ask is most oposums, like other wild animals, become cantankerous after they get to a certain age. they just don't really want to be domesticated. i am not as intimate with mine as you are. he is a free roaming pet who comes in my garage and eats and just hangs out. i have, however raised baby opossums and turned them loose when they started to get a bit feisty.
We don't know her age exactly but we got her a year ago this month. A dog killed her mama and when my dad went outside to see what was in his yard, he saw it was a dead possum and then noticed the babies in her pouch. There were 12 of them and since my dad couldn't care for that many babies, I took 2, a boy and a girl. The boy, Al, did really good for a while but he just started getting weak and wouldn't eat very much and he died. Our girl, Samantha, started out kinda slow but she did really good and now she is getting pretty big. She roams around the house with me during the day or sleeps in the corner in a little cardboard box with her blankie. At night she sleeps in a large cage in the living room.
As you can see in the pics, they were very small when we got them so I don't think they were very old. So they may have been born in July which means she's a bit over a year old.
I had planned on letting her go when she was big enough but her tail was broken when we got her, probably from when the dog killed the mama and she gets hung up on things and can't get loose, and also after a while I noticed one of her eyes is not quite right and I am afraid she might be blind in it, possibly from the dog attack also. She is also quite mommy-ized, she stays with me most of the time she is running around the house. I have to always watch my step because either her or the cats are always around my feet. She also has no fear of cats and in the wild that could be very dangerous.
So I guess she will remain with us her whole life, which will be longer than in the wild. Possum life span in the wild is maybe 1 year, the lifespan of one not in the wild is 2 or more years.