The family's emotional & mental outlook is no doubt helped by the fact that their child still looks more-or-less like a normal baby. The bonding is very strong on that level. And she's easy to move, control and care for, compared to a normal 12 year old sized child who would have the same developmental problems & health issues.
I know a family that took care of a pair of ancephalic twins for nearly 8 years. The twins never learned to respond to their names, sit up, crawl, feed themselves etc. All they could so was eat, poop & feel pain. The biological parents (relatives of theese people) had effectively abandoned the twins at birth. The family finally had to have them institutionalized because they lived in a very small house and the twins had effectively outgrown the disposable diapers they could afford to buy and were so heavy/large, it was difficult to move them enough to prevent bed sores from developing, not to mention cleaning them. Their entire lives revolved around feeding, changing & monitoring the twins, and it finally got too much for them. They're in a decent nursing home about 300 miles away, and their great-grandma (who was the one who took them in and their primary care-giver) goes to check on them once a month.