My Dad fell in the bathroom last night. He was not seriously hurt either. He doesn't have a clue that it happend. Mom is the one that is blaming everybody and everything. It is very normal. In their world it is impossible that something just happened to them without it being somebody else's fault. As much as it annoys us it is the way they think. When Mom does this I just say.... "Sorry Mom, it won't happen again."... and then go on to another subject. That gives her a moment of validation (they very much live in the moment) and the incident is soon forgotten... usually. There are those things she hangs on to for a while but eventually she will let go of them with a little creativity on our part.
I am so very glad your Mom was not hurt. The fall and ensuing commotion has probably knocked her off balance for a short time but she should bounce back. As soon as the hoopla dies down she will get beyond it. You might want to tell the other to not continue to ask her about the fall. If she brings it up that is different but you can tell if she is ok without asking how she is feeling after the fall. Just a few tips that work with Mom... most of the time! Nothing is definite in ALZ