You don't.

First, PA does not have a statute allowing for emancipation; if it does happen it's at the county level.

Second, emancipation does not mean the child is allowed to move in with someone else. It means the child has proven to the court that s/he is capable of being fully self-supportive.

Finally, a pregnant minor indicates to the court that she needs more - not less - adult supervision.

Unless your Mom agrees to your sister moving in with you, it's not happening.

Sorry.