She is much stronger than Thor due to her sheer physiology. Children in the same family don't often have equal strenght, even if they trained the same way.
Asgardian Physiology: As the eldest child of Odin, Hela had tremendous superhuman abilities and supernatural powers, far superior to those of almost every other Asgardian, including Thor at full power. Heimdall believed Hela was sufficiently powerful to conquer the entire cosmos.
Now, Hela turned out to be too powerful, and as Odin's true heir, she was tied to Asgard. Thor realized he was not going to be able to defeat her, and in an interesting turn of events, he ended up restoring Surtur's power by having Loki drop the crown in the Eternal Flame.
Odin's enchantment on Mjolnir in the beginning of Thor made it so only those worthy could wield its power. The most plausible explanation for Hela being able to hold and destroy Mjolnir is that Odin's death weakened the enchantment and she was too powerful for it.
Stormbreaker can summon the bifrost and Hela is stronger in Asgard. Thor can teleport her and himself and open her chest killing her, or cut off her limbs ir head. Plus, Stormbreaker is stronger than Mjolnir.
Unable to kill his own daughter, Odin defeated Hela and imprisoned her using his own power to keep her at bay in another realm for eons. During this respite, Hela attempted to escape imprisonment in Hel and was near successful.
Naturally, the clearest and most obvious reason why Thanos would win in a fight with Hela would be his Infinity Gauntlet. In the Mad Titan's possession, it would be incredibly difficult for Hela to defeat him either in a straight fight, or some other means.
In a moment of wistful affection for his girlfriend, Thor asked his trusty hammer to always protect Jane, and in doing so unwittingly enchanted Mjolnir to do just that. Just like Thor's father Odin once enchanted the hammer to only be lifted by someone who is worthy, Thor cast a spell that let Jane use its powers.
Stormbreaker has the additional power to summon the Bifröst, allowing Thor to teleport anywhere in the Nine Realms. Screen Rant has identified Stormbreaker as the more powerful of the two, based on this ability, as well as it being a much larger and edged weapon.
Nowhere in the movies is Superman able to tank a bladed weapon from a superhumanly strong opponent. Assuming we're talking DCEU and MCU versions, then Hela wins this. Yes, she's not as fast as Superman and he'll give her quite a thrashing, but nothing Superman does will keep Hela down for long.
If so, why? Surtur was pretty much well known among the Asgardians as the guy who'll commit Ragnarok which means the end of Asgard. Basically, he's outright a real threat to Hela's power. Hela had every right to fear him because he does has the power to end her at full power.
Yet another one of Odin's sons turns out to be an extremely powerful god. It is believed that Vidar was the strongest among all men or gods, except for Thor. He proved his power during Ragnarok when he killed Loki's giant wolf-son, Fenrir.
Hela appears in media set in the Marvel Cinematic Universe (MCU), portrayed by Cate Blanchett. This version is the daughter of Odin instead of Loki, and the first Asgardian to wield Mjolnir.
In the comics everytime Jane became Thor, Mjolnir purged her body of toxins. In her case those toxins were the chemotherapy drugs that were at the very least keeping her cancer in check. So everytime she became Thor her condition became worse.
When Thor and Jane are still dating, Thor asks Mjolnir to always protect Jane no matter what. This oath alone speaks to the deep connection between Thor and Mjolnir, which rarely finds others worthy of wielding it. To keep its promise to Thor, the hammer calls to Jane telepathically, guiding her back to New Asgard.
Eitri appeared before them and learned that Thor needed a weapon, so he decided to forge Stormbreaker. With Thor and Rocket's help, Eitri opened the cage around Nidavellir and re-lit the forge, melting down ingots of Uru and pouring it into a mold.
Thor: Ragnarok gradually reveals the truth about its version of Hela; she is Thor's older sister, and her power seems at least equal to that of Odin the All-Father itself, explaining why she is able to destroy Mjolnir with contemptuous ease.
We can conclude that Hela is not more powerful than Odin. Its just that Odin was already weak and she waited for Odin to die before she tried to take Asgard.
So while Zeus' best feat is defeating a mountain-sized monster, Odin's best feat is defeating a monster as big as nine worlds. Odin outclasses Zeus in intelligence, versatility, strength, and weapons. Zeus simply can't compete. The winner is Odin, All-Father of the Æsir.
Mjølnir is a powerful enchanted war-hammer forged by the Dwarves for the Asgardian Royal Family, and was used by Odin before he passed it down to Hela and then Thor. The hammer was used extensively by Thor as his primary weapon until it was destroyed by Hela in 2017.
