My stepdaughter is also vegan. Is it a coincidence that she moved to Spain this summer?? I think not. She simply cannot tolerate the cold.
However, while she was living here, I strongly encouraged her to get some thermal underwear. What can I say? She is young. She is not sporty. The idea of thermals had never crossed her mind, not for regular wear. She looked at me as if I were insane.
However, during the polar vortex, I got well and truly sick of her complaining. So, I went out and bought a bunch of thermals for her and because things had become intolerable and she could not crank the heat high enough even indoors, she finally put it on. Wonder of wonders -- for the first time in 5 years she could stand to be outdoors for longer than 10 seconds!! It truly helped. I got the stuff from MEC (similar to your REI) and chose the warmest option.
Puffer coats are definitely do-able without down and sometimes even warmer than down options. If she has an insulating layer underneath that also helps.
Sweaters in cotton are soft but generally not super warm and if heavier they can droop and stretch easily. Acrylic can be warm (even hideously so, because non-breathable) but it pills and is static prone. My stepdaughter did rely on it. She also wore a lot of layers -- a jacket over a poly shirt over a thermal tee...I think your daughter is simply going to have to embrace maximalism in her winter style. It doesn't have to be visible maximalism (maybe) but she will absolutely need layers to stay warm in NH.
Footwear is probably the trickiest area. Again, you'll need to look for highly insulating synthetic socks and they'll need to be wicking in some way because rubber and plastic boots are not as warm. Goretex might help, or those Bogs boots that have insulation in them.
Handwarmers might also be a good idea. Also, ear muffs.
Good luck. It's not easy watching them freeze.
