Oh Anna, I know how devastated you must feel. As far as what you should do, just let her know how badly you feel about what has happened. I know you have already done that, but as others have said a note or another call. Just so she is aware that you don't take the situation lightly. Then try to comfort her on the loss of her pet. Afterall, you are one of the people who truly understands the depth of a relationship a person can have with a pet.

But please do not feel guilty any more. It was an accident and not your or Roxey's fault.