Residents and citizens of the United States pay income tax on worldwide income. You will report the gain on the sale of the property on 4797
You may also need to report the rental income (after her death) on Form 1040 (Schedule E) . That may have been true for 2006 as well as 2007 depending on when you inherited the property.
According to Article 6 of the Tax Treaty with Romania the sale of "immovable property" may be taxed by Romania as well as the United States. Income tax paid to Romania will be eligible for the foreign tax credit on Form 1116 .
The value at the date of death of the property you inherit is not taxable, your accountant is correct.
The income from the property is taxable, once you are the owner.
Any gain from increase in value after you inherited is taxable. Your cost for selling is the value of the property at the date of death.
I hope this helps to clarify for you.