She'll probably need a lightweight waterproof turnout sheet (no fill) and medium weight (200g fill) waterproof blanket to start. If she's thin skinned like a lot of TBs and it gets really cold, she might need a heavyweight too. I think I sold all my 78s last year, but I'll check and see if I have any extras! Ebay is a great place to check too, especially this time of year when most people aren't thinking of buying blankets yet.
I've spent most of my life riding horses. The rest I've just wasted.