I am looking for who makes the smallest plastic mountaineering boot. My wife wears a 3.5-4, and it seems REALLY hard to find anything to fit her. She also gets extremely cold feet, so wanted to find something plastic to replace her leather boots, that don't really fit anyway.

Is she a 3.5-4 in US Wms, US Mens, UK?
Check Sportiva / Koflach Degre's - they have pretty small sizes. My wife is pretty tiny @ 5'0' - is a Wms US 5.5 and wore Degre's for a few years.

She wears 3.5-4 women's. she has scraps t2 tele boots that are 3.5 but too low volume in arch. Ideal would wide with a low volume heel.

She wears 3.5-4 women's. she has scarpa t2 tele boots that are 3.5 but too low volume in arch. Ideal would wide with a low volume heel.

I don't think you're going to find any mountaineering boot that small. Sounds like sticking to a tele / AT boot remains her only option.