I had a similar experience last week. I was cooling down my over50s class with walking round the room in a circle, sidestepping then walking backwards. One of the ladies (she is in her 80s!) tripped over. I felt awful, it is a huge class 40-50 people. But I had to just keep going, after checking she was ok (she just bruised her butt). Hopefully in a couple weeks I will feel 100% confident again, but with older ladies I worry about brittle bones etc.
When doing 36 I fell a few times learning bird pose, but my worse thing was I was trying so many times I ended up with loads of bruises on my arms from trying to balance, very embarrassing!
You did the right thing speaking to the client, if she is fine, then just keep teaching and enjoy it, accidents sometimes happen however much cueing and CRC you do.