Whilst I never kept a diary I believe I was home alone on occasions at 12, minding my younger siblings. That said that situation was less dramatic than you describe. Usually my parents would be back before I went to bed, and it ws not 6 days a week.
It does seem unfair on the girl you describe, being apart from her parents for such long times, left to amuse herself 6 days a week. At that age there should be guidance and security. Maybe as mentioned, it is out of necessity ?