from a rp point of view, her power comes from her connections with:
- the imperial empire
- the thalmor
- the thieves guild
- the dark brotherhood
So you could essentially nullify all of those by:
- Completing the stormcloak civil war questline and booting out the imperials
- The stormcloak questline AND kill off all the thalmor in the embassy and northwatch keep
Spoiler just ignore the thieves guild as their luck will expire anyway
- and chose to kill the dark brotherhood
Not to be off topic here, but the Stormcloaks winning the civil war is exactly what the Thalmor want. They want Ulfric to weaken the Empire's grasp on Skyrim/Tamriel. In fact, there's a ledger that can be found in the Thalomr Embassy that clearly states that Ulfric is nothing more than a catalyst for the Empires defeat and the Aldmeri Dominion's victory. So by helping Ulfric and his rebellion, you're actually helping the Thalmor tighten their already strong grip on Tamriel.
Back on topic. I don't believe there's any real way to bring Maven down. The best you could do is follow what Ben42 said. Also, If you side with the Imperials, Maven will become Jarl of Riften. If you really want to screw her, then that's the way to go.
