Sniffles aren't directly caused by cold air. It's a virus passing around. So wash hands a lot, don't allow them to share cups, etc. Same as anywhere else.
I don't nurse outside in the winter. I go inside. Besides, babe is way too distractible at that age. There are some places I just don't need cold air! LOL
For outside, dress baby warmly, put her in the wrap. See if you can buy a large polar fleece vest. You can typically find them cheap. Put it on over both you and baby. If it's really cold, you can also try putting a blanket wrapped around them and then the vest over them. You then put on a coat and you should be okay. If it's terribly cold, just go inside. No one expects your baby to be outside in bad weather.