The Alternative timeline

Emma, and Isaac one of the few high schoolers. Being best friends and in their first semester-when a storm hits gas made from scientists secret experiments. It hits the whole town and zombies break out, Emma wasn't infected during the storm neither after. Isaac was, the gas made him weak and when she had left one day to meet up with friends for grouping he was bitten somehow.
Now she has to figure something out, can she be infected? what will she do with her zombie best friend?