Girlfriend wants to become a welder

So, I'll preface my saying that I am not personally a welder and I don't know much about the trade itself. My girlfriend (21F) has aspirations to be a welder, either in NYC or the Midwest (depends where the universe decides to take us). She has some hands-on welding experience from high school (finished on top of her class), and has some kind of OSHA certification.

I have done a fair amount of research about welder/iron worker's unions in NYC, and have heard that unions are the most cost effective way of getting into the field (there is no tuition, you just max have to pay equipment fees), since those technical schools, like Apex or LincolnTech, are ludicrously expensive.

Can anyone break it down on how it works? Like provide some kind of simplified road map? I want to support her in any way I can. If anything I just said is bogus, feel free to call me out, as I am a layman and trying to understand how all this works.