Training is one thing--criticizing is another.
I think it would be fine, as the trainer, to say, "Oh, I noticed that you hadn't read the whole e-mail. Be sure to slow down--if you think about it, you'll have spent more time already just figuring out how to return the extra one, etc., than you'd have spent being careful in the first place. And by the time you actually return the item, it'll probably be 4 times as long as reading the email carefully."
And I'd follow it up by saying, "I encourage you to take the time you need to be careful. It's a form of sticking up for yourself, to insist on slowing down enough to be mindful about what you're doing. Protect yourself from mistakes, from any reputation loss that comes because you're rushing. Don't get so wrapped up in rushing that you set yourself up for this sort of incidental time cost."
But that's not the same as (to use the OP's words) "calling her on it."
(and if "being responsive" is something she's working on, that might have led her to rush a bit with this--to be responsive)