Request #526 From Savanah

I remember reading this in middle school which would have been 2013ish, which means it was age appropriate enough to be found in a middle school library. It was a teen romance with comedy elements about a girl who is brought back to medieval times with her friends and is swept off her feet by a mysterious black knight who never reveals their face (I think it was a big shock on who their identity was, but I don’t remember). Her friends feel betrayed because I think the knight is supposed to be evil or something? I also specifically remember a portion about cow manure being used to create an explosion or energy. Any help would be appreciated!