I think if it was that important to you to have an answer, you would have spoken with the teacher in person..
But I also feel you are totally over reacting. Your daughter tied the shoes together and I am assuming must not have had a problem getting around if no one, noticed they were tied together.
I emailed her back the same day and said "And you allowed her to walk around like this the rest of the day? Isn't that dangerous, don't you think?",
I would not reply either since it is a rhetorical question that you asked.. ..
You owe her an apology for your tone. Remember teachers are not there to make sure children hurt themselves.
They are on your side. She has way more than 1 child to look after and at the end of the day it can be a bit busy.
Teachers are professionals just like a Doctor or a Judge. show them the same respect, you want them to give you.