It is about 140km by train from Tianjin to Beijing,
Do you mean she will go to Beijing Railway Station from Tianjin, or from Beijing Railway Station to Tianjin? And what kind of train will she take, bullet train or the ordinary train?
Usually, people take bullet train from Tianjin and reach Beijing South Railway Station. Some slower trains may reach Beijing Railway Station. You'd better ask your friend which train does she take.