I know this is frustrating and I can breath a sigh reading that Lexi is ok and nothing serious happened.
Training is an on going process with no perfection. But...I do agree with the other posts in regards to using a longer leash/tie out. It does work. Infact, I need to practice this exersize myself with Schatzie. She is becoming let's just say a tad attitudish!!
I have read many books and watched training shows that highly recommend using this process in training the "come" command.
Good luck and hugs to Lexi.