Why was Ahsoka involved in the Siege of Mandalore?

Question

While looking into details about Ahsoka Tano, it seems there was a plot slated for the end of the season 8 of The Clone Wars TV series (which was never produced), wherein she leads a Clone battalion during the Siege of Mandalore. This event was later referenced in Rebels TV series as well as the Ahsoka novel, so it's fairly canon.

My question is: why was she involved in this event at all, particularly in a leadership role? Being a Jedi Padawan gave her the military rank equivalent of Commander, but this took place after she had officially left the Jedi order (which came after her being officially expelled from the Jedi order). Is there any canonical reason given as to why she still had the authority to command a Republic battalion, or who gave her the mission to hunt down Maul, and why she was involved at all?

Answer 1

It's not entirely clear, but it seems like her ties to the Order were strengthening

Dave Filoni discussed his intentions for the unfinished episodes in a 2016 interview with IGN:

What was significant about that was that it was the story that was really going to draw her possibly back into the Jedi Order, because the motivation around this conflict with Maul was her knowing the personal history between Maul and Obi Wan

[...]

[Ahsoka] was actually planning with Obi Wan and Anakin the capture and attack that would get them Maul, because she had figured out where he was towards the end of the Clone War. But before they can go through with this plan together, Obi Wan and at one Anakin get called away to Coruscant to save the Chancellor, which leaves her with Rex – and some other exciting characters – to basically go and deal with Darth Maul, once and for all.

So, according to Filoni, Ahsoka's involvement went something like this:

• While out doing her own thing in the galaxy, Ahsoka somehow uncovers intelligence on Maul's whereabouts
• She reaches out to Anakin and/or Obi-Wan with her information
• For some unknown reason, the Jedi involve Ahsoka in the plan
• Anakin and Obi-Wan are called away on more urgent business¹
• Ahsoka carries out the mission alone (albeit with Rex and a bunch of clones)

Some of this was incorporated into the canon novel Ahsoka (emphasis mine):

She'd walked away from the Jedi Temple with nothing but the clothes on her back and had struggled for a long time to find a new place in the galaxy. When she had found a mission, when she had reached out to her former master for help, he had reached back and given her the Jedi weapons to do the job.

^Ahsoka

If Filoni's plans are to be taken as canon, the most likely explanation is that Ahsoka was given authority over a contingent of clones (including Rex) as part of a soft return to the Jedi Order; perhaps the Council wanted to draw her back into the fold.

What is clear, however, is that Ahsoka had no formal position in the Grand Army of the Republic; this is mentioned explicitly in the novel:

She wasn't a commander anymore, even though the battalion still treated her with the same courtesy they always had, because of her reputation.

^Ahsoka

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¹ Wookieepedia speculates that this was the mission in the prologue to Revenge of the Sith; I'm not sure if that's substantiated but, given the timeframe (Order 66 occurs while Ahsoka is fighting Maul on Mandalore), it seems plausible.

Answer 2

There are multiple reasons. SPOILERS FOR SEASON 7 OF THE CLONE WARS

1. Even though Ahsoka was only a padawan when she left the Jedi Order, the Council said that they would have made her a Knight had she stayed. And, it was explicitly said her skills matched many Knights. Plus, the Siege of Mandalore was one of the last battles of the Clone Wars and the Jedi were spread really think throughout the galaxy. They didn't have anybody else to send. Anakin and Obi-Wan were sent to the Battle of Coruscant. However, they could afford to send Ahsoka, a former Jedi who had the skills but was not involved in the war anymore.

2. Ahsoka had a connection to Mandalore and the Death Watch. In season 3, she and Lux Bonteri stumbled upon the Death Watch camp on Carlacc. She even engaged both Pre Vizsla and Bo-Katan Kryze in combat. Bo-Katan, during the last months of the Clone Wars, lead the remaining part of Death Watch that was not loyal to Maul. They were known as the Mandalorian resistance. Death Watch was split into Maul and Bo-Katan's factions after Pre Vizsla's death at the hands of Maul. Bo-Katan remembered Ahsoka due to their encounter, and later, specifically, sought her out to lead the Republic forces on Mandalore. She specifically referenced their encounter on Carlacc when another Mandalorian asked her whether Ahsoka was the Jedi.

3. This is all shown in Season 7. Ahsoka was on Oba Diah due to trouble with the Pykes and found information regarding Maul. It was some business with her associates running spice and stuff. Now, the Pykes are part of the Shadow Collective, a large criminal syndicate that Maul controlled. So, she accessed the Pykes' database and found Maul's location; Mandalore. Bo-Katan needed this information to pinpoint Maul's exact location, Sundari, Mandalore. Since Ahsoka was the one who helped them find Maul, obviously, she was the one for the job.