Don't beat yourself up, the crisis is over now.
Thankfully your vet was smart enough to put her on penicillan (I know of a horse that died from secondary lung infection, after choke, because the vet didn't put it on antibiotics).
I know that I will be put on the firing wall with a bunch of beet pulp machine guns pointed at me, but choke is why I will never feed beet pulp -- never.
I have two horses that are insulin resistant and a third one that has four molars missing but, beet pulp will never be found in my barn.
I have yet to hear of a horse choking on rice bran. All my horses get varying amounts of pelleted rice bran. They all love the taste so its easy to mix their supplements in with it.
Rice bran is high in healthy fat, provides a cool energy to the horse and no soaking required.
The IR causes one horse to lose weight, so the rice bran keeps weight on him.
The other horse is a tanker, so he only gets an 1/8th cup of rice bran twice daily to enhance the flavor of the other stuff he gets.
One thing you might want to keep in mind is that, once a horse does go thru a bad choke episode, it can sometimes leave scar tissue which makes choking an easier thing to happen in the future.
Other than that, don't berate yourself, your horse pulled thru and life is good