Mackenzie Shirilla’s aunt tried to defend her niece in her murder case … telling the judge Mackenzie was in “very much in love” with her boyfriend before the fatal car crash … TMZ has learned.

TMZ obtained court docs filed as part of Mackenzie’s appeal of her sentence. She made the case that prosecutors failed to prove she had a real motive to kill her boyfriend, Dominic Russo, and his friend, Davion Flanagan.

Prosecutors used forensic evidence to show Mackenzie was driving a car that was going 100 mph and didn’t apply the brakes before it slammed into a wall, killing Dominic and Davion, on July 31, 2022.

She said the evidence actually showed that she and Dominic appeared to be in love in the days and hours leading up to the crash.

Mackenzie said one witness testified they saw her and Dominic together at 4 AM on the day of the incident.

She pointed out that the owner of a store, where Mackenzie and Dominic often shopped, said the two appeared “very loving” in the months before the crash.

In addition, Mackenzie says her aunt, Candace Shipley, said she spent three hours with Mackenzie and Dominic on July 28, 2022, “as the couple was scheduled to watch her dogs in the coming days.”

She claims her aunt said she did not observe any signs of “discomfort or unhappiness between Dominic and Mackenzie” … and that they appeared “very much in love and spoke about their future plans together.”

The defense also argued that the crash could have been caused by a medical event triggered by Mackenzie’s postural orthostatic tachycardia syndrome (POTS), which is a condition that causes a person’s heart to beat faster than normal.