Custody matters are not permanent so there will be mechanisms to revisit this even if she is unable to reverse this exact order.
However, it is possible to attack a specific order or ruling.
The exact procedure that your fiance will want to pursue here is going to depend on what exactly the order was (and what procedure her ex used in order to get it).
But there are a couple of mechanisms that can apply, including a "motion for reconsideration" filed under PA RCP 1930.2
I would strongly encourage your fiance to at least consult with a local family law attorney to help her put together a comprehensive strategy for how to deal with this matter (again, as I noted above, custody disputes between parents are long term matters and your fiance will want to have an idea for how to go about dealing with this going forward, as opposed to simply attacking one ruling).
The fact that her ex submitted substantial fraudulent evidence in the prior hearing is going to help her in the future (his credibility will be significantly weakened, and it may even make him look less viable for significant custody as the courts are evaluating what is in the best interests of the children.
(The term that may be closer to describe his conduct would be "fraud on the court" - but I would suggest that your fiance focus more on identifying specific evidence and arguments than trying to identify a legal phrase or term).