Sorry for your loss.
Honestly, I think you misdiagnosed.

Sounds more like she had cocci or maybe egg binding/internal laying.
When she *seemed* to have worms again... did you have fecal floats done this or previous times to confirm and ensure you were treating for the correct species?
Are you treating your other birds for the *same* worms? How often is this happening? Or how long was it since you last treated her? Are you treating with the same medicine every time? What is causing your *alleged* heavy worm load, and what are you doing to treat your land/environment?
Many medications, when they expire *may* only degrade slightly in efficacy. They do not usually become dangerous (allergies are a different issue). Also, you state that you used the same expired med 2 days in a row... full dose each time? Could actually been what helped to kill her, as worming an already ill bird can put too much strain on the system.
I don't think the hot peppers kill worms, but maybe make it an uncomfortable environment so that they flee.

I agree that just because birds don't have capsaicin doesn't mean it's safe for them to consume large quantities as it could cause internal burns or ulcers (maybe). We have heat receptors as a means of protection. Pain tells you "this could be dangerous". Why, by the way.. put those heat receptors in the anus of humans?!
One final though... how does a bird get to the point of immobilization from heavy worm load without there being earlier symptoms? Sincere question, just trying to learn here.
I will share that crushed red pepper packets often come for free with your pizza. The hens do seem to enjoy it. But I don't use it thinking it's gonna get rid of my worms. And to be honest, until someone SHOWS me their lab report with specific counts both before and after hot peppers/pumpkin seed/DE... I say hog wash/snake oil.
5 teaspoons at one time of anything, much less peppers seems like an extreme amount to me, for any chicken!

How much can they even fit in their crop? Seriously, when my Hubby cooks spicy peppers, it feels our house with very lung/throat irritating fumes... He usually does it outdoors now. I hope you never do that again... we all have to learn somehow and start somewhere though, so I don't mean it to put you down! I'm sure you did your best with the information you had at the time.
To answer your original question... Yes, I think you contributed to or hastened the death of your bird by force feeding peppers (especially if they were in dry powder form), and maybe too much wormer.

But she may not have made it anyways, and you might feel worse about doing nothing.
There are other external parasites that if out of control could also contribute to the weakness. There really isn't enough info given for a true assessment...
Better luck next time!
