My cousin died in Virginia while living there for 15 years with her second husband. The will was changed 3 months before her death.

I'm sorry to hear about your sister's passing.  People do change their minds regarding the disposition of their assets at death.  If she left everything to her spouse, that would not be considered unusual.  You'd have to prove that your sister has insufficient mental capacity to understand what she was doing when she executed her last will.  That's a really tough thing to do becasue under PA law, the necessary capacity in order to prepare a valid will is a relatively low bar.  Estate proceedings can be time consuming, costly and emotionally costly.  Unless there's a great deal of money at stake, you may not want to attempt to face these hurdles.