Okay, I finally got her installed and unlocked.
I did a number of things, and I'm not sure how many of them were actually necessary. There's one step I think was key. I'll list the other things I did first at the end of the answer.
Install From Manage Game
I found this advice from Undead Sanya (who appears to work for the developer, Undead Labs) from this forum thread:
- Go to your X1.
- Highlight the downloaded 'State of Decay: Year-One" in your Games section.
- Hit "Start"
- Scroll down and click on "Manage Game"
- Look for "Add-Ons" just to the right of the main image. You should see Breakdown, Lifeline and Prepper's Pack available
- Click on them and Install.
- Go to Breakdown and look for Gurubani.
- If you find her... yay!
Although Gurubani was not showing up as DLC in the marketplace, she did show up on the "Ready to Install" section of the Manage Game hub. Once I selected her to install here, things changed. The next time I started my game, instead of seeing message asking me if I wanted to install her, I saw a message thanking me for getting the game and saying that I could unlock her in the main game via radio once I had established a base.
After getting to the church, you don't get the radio until after you complete the first survey request. Once I had done that and returned to base, I saw the "Bonus Survivor" option on the second radio tab. Clicking on this resulted in Gurubani joining my group, without me needing to go pick her up anywhere.
I checked, and she is also now available as a starting hero for Breakdown.
Other Things I Tried
Here are other things I tried. None of them solved it. It's possible some of them may have been needed as prerequisites to what eventually worked.
Saying yes to the in-game prompt to install her didn't appear to accomplish anything.
As indicated in comments on the question, I was initially unaware I was supposed to import my save game to unlock her. After unlocking all the Breakdown heroes other than Alan (cause that's a freaking hassle), I imported my old save game from the 360. I was disappointed that this un-unlocked (locked? relocked?) the Lifeline heroes that were added to Breakdown. Luckily, none of them take much effort to unlock. She was still unavailable as a starter in Breakdown.
That same thread I linked above took me to the official Year One: Survival Edition FAQ on the Undead Labs forums. There, it said to do this to unlock the Prepper's Pack, saying that these same steps were needed for Gurubani:
- Install the whole game and the DLC.
- Note that you get a thank-you message on the way into the game.
- Play to the point where you have a stable "base" in the game. (In the core game, that means getting to the church. In Breakdown, it means joining a community. In Lifeline, it means rescuing Black Friday.)
- The Prepper's Pack now appears as an option in the Radio Menu.
- Select it, and the weapons are deposited in your Supply Locker, while the vehicle is spawned nearby and marked on your map.
I tried that and it didn't work, but in retrospect I probably didn't fully accomplish step one. I also don't have the Prepper's Pack, whatever that is.