Welcome to the forum, speidel! Don't worry too much about the 'extra' hair right now - nature has a way of making sure it will all shed exactly when your horse needs it to! Just continue brushing and also a rubber curry feels soooo good to your horse right now as well. There's always a reason for the extra hair to stay for a while, and nature knows better than us. Everything in it's own good time.... :)
Until it gets warm enough to give a good bath, I would suggest one of those slick and easy grooming blocks- if you are gentle you can use them on legs with great success! I don't recommend using a curry comb (unless its a really "scooshy soft" one on legs, because there isn't much protection (muscle/fat) on the horses legs, just bone and tendons/ligaments!
If you are trying to get ready for a show, clipping her legs will make them much easier to clean.
Once it is warm enough for a bath, there are tons of whitening shampoos that you can rub on, leave in, and then rinse off for sparkling white legs!