"For the moment, she has a hat."
Translation:Tạm thời, cô ấy có một chiếc mũ.
I beg to differ. "At" and "for" may sound like the way you translate it. But in real usage, at the moment can last longer than for the moment.
For instance, I can't see you for the moment. = I can't now but I will see you soon. I am happy at the moment. = I am happy now and will be happy after.
I don't think we should stress the difference between hiện tại and hiện thời here because in vietnamese, we tend to simplify adverbs. In fact, it will be best to translate "cô ấy đang có một chiếc mũ". "Tạm thời, cô ấy có một chiếc mũ." sounds very awkward/archaic to me. Just my 2 cents,