It’s called fashion, look it up
Can you imagine how stressful it must be to present something to 230 complete strangers? That’s what this person’s coworker had to do, and the anxiety was slowly chewing on her brain. Things got so bad that she didn’t realize she had on two different shoes during the presentation.
She had no idea why people were staring quizzically at her, but she took it in stride. According to the OP, she actually nailed her presentation, mostly because she didn’t realize her mistake until after it was done. At least now she was sure that they were silently questioning her appearance and not the content of her presentation.