Hello I have returned, taking notes on what people have said + providing a bit more context on the character's situation since I posted this in the middle of the night ><"
The woods/forest would lean more temperate but be closer to taiga in precipitation, their mother did teach them some short-term survival skills but definitely not something that would last that long. The two of them already had issues with their parents and one of them does have a habit of thievery which could both play into the issues of food, hygiene(maybe? thinking in regards to the menstruation point), and other people.
Speaking of other people, there is a bit during the time frame where a third party interferes in the siblings situation, which is where the idea of fairies kidnapping them comes up. My outline/notes currently has this part written down as "While lost, a strange magic woman locks the two in her 'abode'". I'm not sure if she counts as an authority or parental figure, especially since I currently have it so she's been dead a good couple of years at the start of the story.
A lot of this stuff is rather early stage so I do apologize for lack of details that come up, but it is very fun to hear other peoples suggestions and all of the new reading material I have. ^v^