When I snapchat one person, it is always black but not for anyone else? help?

Whenever i snapchat this one person, all i get is a black screen back. she can see my snaps, but i cant see hers. Also, i tried to reinstall but that didnt help at all. i also made a new account and added her and it still didnt work. everyone else i snapchat doesnt have any problem. help?