Reddit mentions of Ladies Chunky Hand Knitted Twist Beret with Matching Flipmit

Fleece lined tights would be a great smaller gift to give your friend. They are black and opaque, which I think would be quite suitable for professional attire aaannndd they have the warm fuzzies of a sweatshirt hugging your legs. Be sure to check the size charts of any of these products so you get her the right size.

I feel like clothes wise, she should be fine with anything she brought from California. Skirt and a suit jacket? Well, put on those fleece tights. Thermal underwear under clothes can also keep you very warm. Scarves can help with drafty environments both indoors and outdoors. A long pashmina can pretty much be used as a blanket without looking crazy.

Once it starts snowing she may want to get snow boots, so she can switch up what she's wearing on the streets vs. indoors. I love anything by Sorel, these boots are warm, waterproof, and cute!

Accessorizing and layering is the biggest part of staying warm in the winter. You could also go the mom route and get her a nice hat and gloves set so you know she's not freezing her fingers off! Hopefully I provided you with some helpful options. You're a very kind friend to do this for your friend's birthday!