My babies used to be the same way. The best advice I can offer is to be consistent, it really does pay off. It may take a while for your little one to realize that she has to use it no matter the weather conditions, and it probably won't be any fun for you either -- but, if you stick with it she will learn.
When it rains they are so funny because they know they have to use it, so they are really quick at it when it rains. When it snows, I just shovel a clear area for them to use it in.
Mine still don't love to potty in the rain or snow, but they know they have to. Consistency is the key -- and lots of patience!
