Ignoring most of the “she’s a Mary Sue because… reasons!”
But Lightsabers have always been shown to be heavy. It was a major plot element in the first six films that Vader was the only one strong enough to wield a lightsaber with one hand.
Is that still canon? Maybe not. But lightsabers have never been described or depicted as light.
But keep looking for reasons to call Rey a Mary Sue despite her similarities to Luke and Anakin.
As for the question of how she resisted the mind probe, it’s a common trope that Rey quotes… about doors being able to be walked through from either direction when opened.