Is Odin's daughter Hela stronger than the Infinity Gauntlet and Thanos? Is that why she flicked it over as if it was worthless or did she do it because she knew it was a fake?
She knocks the Infinity Gauntlet over and off of its podium because it is fake, as she says when she does it.
Hela walks towards the Infinity Gauntlet.
Hela KNOCKS the gauntlet off its pedestal.
Hela (cont'd): Most of the stuff in here is fake.
Taika Waititi, the director for Thor: Ragnarok, explains in an interview with Cinema Blend why Odin had the fake Infinity Gauntlet in the vault in the first place.
That came about because in Thor 1, the reason that it's in this movie is because someone who went through that movie, frame by frame, looking for Easter eggs was like 'Oh! The Infinity Gauntlet!' And then from that point on, they were like, 'That damn Infinity Gauntlet, what are we going to do with that thing?' It's like, there, but it also [exists] somewhere else in the universe. How do we deal with that? And then we realized like, Odin... Hela goes through and she goes, 'Fake. All of that stuff that's in here is fake.' Basically the thing we were trying to go for was that Odin somewhere along the line realized that everyone knew that the Infinity Gauntlet was on Asgard and in the safe keeping of Odin, then no one would come looking for it. So he made a fake one, and let everyone believe... Basically, a fake launch code.
So Odin had a fake Infinity Gauntlet made and let everyone believe it was real. Hela was his daughter, first and only born (for a while), she was being groomed for command and helped Odin conquer the Nine Realms. She knows a lot of secrets that others don't, including Thor, and it makes sense that she does considering the above. Out of universe it is of course a retcon of an Easter Egg explained above by Taika but it makes some sense in universe to.
For your main question we don't actually know if she is stronger than Thanos and the Infinity Gauntlet or not. Thor managed to almost kill Thanos in Avengers: Infinity War with his power and Stormbreaker but Thanos is taken by surprise and Thor has a Thanos killing kind of weapon. Then in Avengers: Endgame Thor isn't really the same as he was having become severely depressed and Thanos also doesn't have the Infinity Stones for most of the fight. So we can't really compare Thor vs Thanos with Thanos vs Hela taking into account the Thor vs Hela fights.