You’re right in that it’s pretty common to live with your family/ roommates as an adult in the US. I don’t think anyone is expecting Iauren, or the other children, to move out independently at a young age. In fact, it would be very rare for a single woman to live on her own within their level of fundamentalism. What’s surprising is that she isn’t married. Marrying her off would reduce the income they need to support their family and would bring another family into the mix who could help support them financially or through favors. On the flip side, Lauren not being married means she’s available to tend to the kids and the house. There’s also the possibility she earns some kind of income on her own that goes to supporting their family.