Based on what you've said, I really don't think it's anything you did that caused it.

Chickens are experts at hiding how bad they feel until they feel
really bad, so she very likely had more going on underneath the surface that she was hiding until it got to be too much for her to do so. It does sound like the ear infection was a secondary infection brought on by something else compromising her immune system.
Unfortunately, my track record is not much better than yours on getting birds to recover from ailments like that. It's been very 50-50 for me whether they'll pull out of something when I've brought a bird in to a hospital pen. I think that they're pretty likely to recover when it's an injury, depending on the severity, but because they hide signs of illness for so long, they often are in too rough of shape to recover by the time we are able to detect something is wrong and start acting. Try not to beat yourself up about it
Oh

Don't judge! It was The Lion King. Not the computer animated one that came out a few years back, but the original, hand-drawn, 1994 version. It's always been just such a beloved film to me, but it came out before my time so I'd never gotten the chance to see it on the big screen before. They did a one-week, 30th anniversary re-release in theaters and I knew I just had to see it this time. Man, the tiny details that you miss on small screens, the absolute
artistry of the hand-animation, the depth of the sounds and music, ugh, it was so amazing! A whole new appreciation for the film
But I promise I watch things other than kids' movies as well