There are so, so many differences between the two meds, I don't see how confusing them would be possible short of gross negligence (for context, I am a paramedic, and often administer medications (including both of the meds involved here) in a high stress environment).
Vecuronium (the paralyzing drug) is a powder in the vial and you need to first inject saline it into the vial, shake it up, and then draw out the "reconstituted" med. This is very unusual (there are only a handful of medications in common use that require this, and Midazolam, the intended med, is _definitely_ not one of them). The reconstitution process means she would have had to look at the top of the vial several times, and warning on the tops of vials are, again, very uncommon. Also uncommon is the red cap on the vial.
I have made errors before while caring for patients, and I will likely make them again. I am very aware of the fact that we all can make mistakes, but the number of mistakes that needed to be made here far exceeds the standard of what is reasonable, and is well into the territory of "gross negligence", in my opinion.