Is this a self help eviction?

my sister lives in Philadelphia, lost a rental case to her landlord. long story short, landlord won judgment filed both a writ of possession on and an alias writ of possession.Writ was filed with the courts 5/25/ alias 6/1. My sister mind you, HAS NOT BEEN SERVED EITHER ONE..... Today, landlord comes to the house to change the locks, thank God my sister was there. If she was not served either writ by a landlord tenant officer or sheriff, is this not considered a self help eviction? She is due to move this weekend... What rights does she have right now and what should she do? I live in NY so i am not familiar with Philadelphia Landlord-tenant law, any help you give would be great! Thanks and have a great day!