Terrible news, and I'm not sure what I can say that will help, but I'll try.
Firstly, it's not your fault. That might seem obvious to some, but it's quite common to assume blame, even when reasons says otherwise. Indie had a better, if short, life with you than at her previous home.
Secondly, you might be tempted to get another cat. If you feel up to it, it would be a great idea, but don't let yourself be bullied by anyone either way. I think any cat would be lucky to have you care for them, but only when you're ready.
I don't know how you came to get Indie, the impression is that it wasn't from a rescue (apologies if I'm wrong). If and when you're ready to give another cat a home, I'd strongly recommend a rescue. You can find your nearest here:
http://www.catchat.org/adoption/Whatever you decide to do, and at whatever pace, just remember that you made a positive difference to Indie's life.