The Will should be probated. The executor can make a claim against the sister for rental value of the house and damage to it.
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In PA there are procedures through the Register or Court to compel production of the Will. But if she is executor/executrix named in the will based on what you said she may not do anything. If you think the Will is void for some reason, you need to file a caveat to block the Will. I note that if the Will specifically divides the house 50/50, she may not be obligated to sell it or buy you out; rather, just retitle the Deed 50/50 and then you will have to proceed in court to force the partition and sale of the house. You need to bring a copy of the will and check the recorder's office and obtain a copy of the deed (if you have one from before the owner of the house died do not presume it is current as a new one could be on file) and then take a copy of the Deed and Will to an attorney to review and discuss procedural options and costs.