We've established that she's an temperature regulated exothermic organism, so three layers will be good down to -10C whatever those layers are.
I would be willing to allow Cat's patches of fur as a layer, if your paws are furry then no need for gloves, if you have a furry neck, no need for scarf, that's a layer.
Common clothes, down to 0C
Fur down to -5C
A cloak would be enough to get the third layer, you can buy that in Phandalin for 20% over.
Example down to -15C
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Leather Cloak 12sp, 3lbs
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Scarf, wool, 6sp, .5lb
Gloves 2sp, .25 lbs.
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Common clothes with boots
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Wool Stockings, 1sp, .25lbs
Mamillare, 3sp, .25lbs
Panties, 1sp, .1lbs
Arctic gear: fur lined jacket with hood, fur lined pants, gloves and boots with scarf, face wrap and goggles with common clothes underneath would itself allow -40C travel, add a layer of undergarments for another -5C
Undergarment layer counts as well, For instance, socks, underwear and mamillare
Ashley has that, a robe and a cloak with gloves as well.