Answer:
The closing date (August 1, 2019) is considered the appropriate ending date in order to determine if the residence had been owned and used by Danielle as her principal residence for at least two out of the five previous years.
If Danielle met the requirements to use the § 121 deductions, she will not have to pay any taxes for the gains generated by the sale of her principal residence. § 121 allows single filers to deduct up to $250,000 of their gains and $500,000 for joint filers.