My father passed away and my mother sold their property in DR and will be receiving a transfer for about 90G .
Does she need to report it.
She is a US Citizen.

This is probably considered to be an inheritance, so no taxes are due.

She MAy need to submit Form 3520 to report the transfer, but that is an INFORMATIOn return only.

She may have to report a capital gain, if the proceeds from the sale of the property exceeds her tax cost basis. Determining the cost basis depends on how the property was titled. You say it was "their" property, so assuming the property was jointly held then her cost basis would consist of her original half of the purchase price plus the half she inherited when her husband passed away. The portion she inherited would have a cost basis equal to half the fair market value of the property as of the date of death. But if the property had been held in his name only then she had no previous ownership and inherioed the entire property upon his death - which means her tax cost basis is equal to the fair market value as of hs date of death.