I think Mabel is going to be powerful somehow.
In the very first episode we see that she has attracted a bunch of gnomes intent on having her, specifically, as their Queen for all eternity. She is the one to defeat them with the leaf blower.
Gideon in the next few episodes becomes intent on being Mabel’s boyfriend. This episode is called “The Hand that Rocks the Mabel” a play on the phrase “the hand that rocks the cradle is the hand that rules the world” (HMMM who ultimately choose the world’s fate?) At the end of this episode, she was also the one to ultimately defeat Gideon. Using the amulet.
Another thing about Mabel is her matchmaking abilities. She says that she has never had an unhappy customer. And it’s proven true! She has matched Soos with somebody, and managed to match several teenaged friends into happiness. Heck she stole love potions from a love god. And to good effect! She also successfully cured Stan’s fear of heights. In “Irrational Treasure” she also manages to solve most of the mysteries by being a dork. And becomes an official congress-woman.
The next episode is called “The Time Travelers Pig” which is interesting. Since the pig belongs to Mabel. It’s also interesting that Mabel was literally the only variable that would have made the outcome of Wendy getting hit in the face any different.
However she has yet to have a successful romantic relationship and gained a fear of heights herself. temporalgearshift noted that she seemed to have an equivalent exchange thing going on. They've also noted Mabel's symbol being a shooting star and the possible symbolism of "wishing on a shooting star" or "shooting stars burning out quickly".
There’s also the entire sweater thing- she’s worn Dipper’s hat, Stan’s hat, and various symbols that represent other characters. This episode she wore a key!
She’s also made a few quotes:
Mabel: Theres nothing stronger than the power of…
Mabel: I am the God of Destruction!
Mabel: And yes I am a witch.