my Pit ate my flip flop!

[Bobcat13]

My 60lb dog ate my flip-flop Monday evening while I was at work. she ate dinner Monday night. I thought all the pieces were accounted for but she had explosive diarrhea with blood around noon on Tuesday. We decided to fast her Tuesday night and she is still acting herself and wanting to eat. shes drinking water and playing. Tuesday night she had a SMALL semi-solid BM (nuggets ) but there were no pieces of the flip-flop to be found. she pooped again this afternoon (wednesday) and it was the same as last night. a small amount of semi-solid nuggets but closer to a soft stool ( TMI LOL) both BMs had blood in it. The blood is red, not dried. shes in great health aside from this, so the only thing we can think of is she ate some of the flip-flops. she is raw fed and has had the same supplements. Nothing has changed. she doesn't care if you touch her stomach either. she seems completely normal aside from diarrhea. shes completely herself.

when is this cause for concern?
how long should she fast?
when should the rubber pieces have passed?