Carole, you poor thing. You are being way to hard on yourself. All of us know you would never intentionally hurt Lexie and she knows that too.
I cannot tell you the times that Rascal has had his tail stepped on because he just loves to sit right behind you - especially when you are in the kitchen and moving around rapidly. He never makes a sound - just parks himself right behind you and in just the right position to be stepped on.
Lexie is going to be so happy to be home and with you. Just wait - she will quickly let you know that all is forgiven!