I was shoveling and chopping ice off my driveway the day before I went into labor with my son. He was a March baby so yes I had been shoveling all winter long - we had upstairs neighbors who were college guys, they obviously had the energy and stamina to do it but they never bothered - and of course my husband shoveled too but we worked different hours so sometimes I had to get it done on my own without his help. I made it until past my due date, it didn't affect my pregnancy at all except probably making labor easier since I was in good shape. It's great exercise with mandatory fresh air -I wouldn't be concerned if I were you. Take it slow, is all.
I live in this wonderful pos state as well lol make sure you are lifting with your knees not your back and small shovel fulls. It takes forever but be careful not to make the path too slippery as well. Either salt it or leave a thin layer of snow for traction
If you're show and steady and don't overwork yourself or fill the shovel up too full you should be alright. But I would make your sister do it, otherwise it'll take you way liner to do it than necessary.