Yes, the sentence is grammatically correct. It means that you have the opportunity to braid your hair without having to pay because your sister is skilled at braiding hair.
Here are a few possible rephrasings:
1. You can get your hair braided for free since your sister is skilled at it.
2. Because your sister is talented at braiding, you can have your hair done for free.
3. Since your sister knows how to braid hair well, you’re able to get