"Poor girl seems to be losing her mind. She’s always losing that necklace it seems. Makes me wonder why she takes it off at all." - Concerned Mother in regards to how absent minded her daughter has become
If a creature is transformed into another creature (say, a human into a dog), then that creature will become more and more accustomed to the new form until a point is reached where reversing the spell is impossible. A second transformation is possible, but the creature will have to go through the whole process again.