Ridecamp: [RC] Head bobbing lame

I had a good ride on my mare today, she didn't seem off.   She didn't want to pick up her right lead right away though, but when she did she didn't feel off.  I cooled her out and fed her her hay.  A water bucket tipped over while she was eating and spilled water all over the place.  She freaked out and scraped her right front leg below the knee, I put some Nitrofurazone on it.  I put her blanket on when she was done eating and tried to lead her and she was limping, bobbing her head up when her right front hoof touched the ground. However it is just a little scrape.  I have never had a horse come up lame from a scrape. It could also be the left hind she is off on.  How can I tell for sure?