She could try Hades, it will give her stuff like the rift strider and power over death/souls so attempting Nyx and tartarus afterwards will be a lot easier
The problem is that he's one of the strongest gods so his trial will be difficult
If im honest, this trial-ark is probably one of my favorite ones, mainly due to the fact that this marks the start where we will see more of the gods, and even after the trial there will be some God POVs which are rather funny