that's not very fair. The logic is sound enough, just the technique isn't. Using feed to make a horse more comfortable in a trailer/box works, using feed to coax a horse over the muddy part of the field works, using feed to distract a horse from clippers etc works. That is because when a horse is eating, it tricks the brain into believing it's safe.
A horse will not eat when it's in danger. The sympathetic nervous system (that controls fight or flight) shuts down the digestive system. Sometimes this can be overcome with a high value food reward, allowing the parasympathetic nervous system to come into play, calming the horse down.
Like all good training though, it's about balance. The OP has over shot the balance on it, although treats as opposed to hay or concentrates are not particularly effective as they don't last long. That's okay though, she realises this which is why she is here asking for advice. We all make mistakes, we never stop learning in the horse industry. The difference between ignorance and stupidity is you can fix ignorance with knowledge. It's great that she's willing and open to learn. Telling her what she is doing is stupid, without offering any practical, non-judgemental advice on how to fix it is a bit pointless.