Sherry Johnston was speaking after it was revealed this week that Palin's daughter Bristol, 17, is five months pregnant by Levi-who described himself on his website as a "f***ing redneck" who didn't want kids.
Speaking from her wooden cabin home in the tiny Alaskan town of Wasilla, Sherry defended Levi, 18, saying: "He might have been a bit of a handful when he was younger but he's now grown up into a caring, mature young man who wants to look after his new family."
Levi and Bristol are now engaged -and the young oil rig electrician appeared clutching her hand as they shared the limelight with the Palins and Presidential candidate John McCain at the Republican convention.
Sherry added: "Levi has barely ever been out of Wasilla and there he was on TV screens aired all around the world.
"He called me afterwards and said it was the most incredible but frightening experience he had ever had."