While her intent was likely not anything done out of malice, I would view it as a huge invasion of privacy. A very similar thing happened to us one time (came home and found her email autosaved in the log in screen) and we hadn’t given her permission to use our computer.
In order to avoid a huge confrontation my wife simply emailed her and told her we viewed that as a breach of trust and wished her well, but told her we wouldn’t be using her anymore. She responded with an apology and said she understood.
We since have made it abundantly clear to new sitters that anything not specifically stated was OFF LIMITS, i.e. our computer, etc.
