PA inheritance tax is due at 4.5% on the value of the house as of your Mom;s date of death. There is no federal inheritance tax and hence no such tax is due at Federal level.
Below is the link to the Brochure for detailed information
Extract from PA State website for your reference-
Inheritance tax is imposed as a percentage of the value of a decedent's estate transferred to beneficiaries by will, heirs by intestacy and transferees by operation of law. The tax rate varies depending on the relationship of the heir to the decedent.
The rates for Pennsylvania inheritance tax are as follows:
Property owned jointly between husband and wife is exempt from inheritance tax.
Inheritance tax payments are due upon the death of the decedent and become delinquent nine months after the individual's death. If inheritance tax is paid within three months of the decedent's death, a 5 percent discount is allowed.