Dreaming about your sister-in-law buying a house can symbolize various aspects of your relationship with her and your feelings about family dynamics. Houses in dreams often represent the self, personal space, or the family unit. Since this house has appeared in your dreams before, it could indicate that this particular space holds significant meaning for you.

Here are a few interpretations to consider:

1. Change in Dynamics: Your sister-in-law's purchase of a house may reflect changes or developments in family relationships. It might signify new beginnings or shifts in your family structure.
2. Personal Reflection: If the house has appeared in your dreams previously, it may represent something about your own life or feelings that you need to address. Consider what this house means to you personally.
3. Desires or Aspirations: This dream might also reflect your own desires for stability, security, or a place of belonging. You might be projecting your feelings about home and family onto your sister-in-law's actions.
4. Connection with Family: Since the dream features your sister-in-law, it may highlight your connection with her and your family as a whole. It could be a sign to strengthen those bonds or to evaluate your relationship with her.

Reflect on your feelings during the dream and any emotions tied to your sister-in-law or the house. These feelings can provide additional insights into what the dream means for you.