Palladium! They make a women's US 4.5, if not smaller. It will either say women's US 4.5 or 'big kids' 3 - they are equivalent.

PALLATROOPER HI-1
PAMPA CUFF WP LUX
PAMPA SHIELD WP+ LTH
PAMPA SPORT CUFF WPS
LEGION HIKER
are leather, no zipper, bifl-worthy boots by Palladium available in W US 4.5

I don't love the US site's search/filtering capabilities so I recommend contacting their support if you don't see what you want - and I know settling for something that says 'kids' on it is not ideal, but I hope this helps some.