This is why I never cover a shift for someone. I will gladly swap a shift with someone but I am not wasting any additional time during the week to be at work if I don’t need to be at work. If you can’t swap a shift with me so I’m not working additional hours in the week then I am sorry, I can’t help you. I work to live, I don’t live to work. Set a boundary now and never take a shift for her again. It is not worth your time of peace.