In a few days the pups would be moved from their private birthing den to the communal den and would be awarded with more freedom than what they currently held. Mabel did not know this, and even if she did it probably would not have changed her current feelings and actions. She was bored of their designated play area and bored of the walks that the adults would take them on and she was bored of always doing what the grownups told them to. Bored.
So when Mom had gone off to do whatever it was that she did during the day and Dad had left after checking on them Mabel had done her best to accost her siblings before promptly walking past their invisible line. Out and away from the small opening and into the now more familiar territory. This was all still boring though, the adults took them for walks through these areas so frequently that Mabel didn't even care that she was now seeing them alone, she wanted something new.
Which was exactly how she now found herself standing on the edge of the well marked borders, Mom's scent freshly marked. The alpha would not be back to check on this area for some time and the pup knew that this was the perfect time. Lifting a single paw she prepared to take a step over into the unknown.