Our dog sitter lied. How do we handle this?

We left for one night. We requested our dog sitter to take care of our animals (dog and cat) from 11:00am friday to 6pm Saturday. She was clear we wanted her to stay overnight. We set the guest room up for her. When we came home it was clear she didn't sleep in the guest room - I asked about it and she said she slept on the couch. We have an outdoor home security system that tells us when people come and go. She left the house friday at 8pm and didn't come back until 1pm Saturday - leaving our dog locked in the house for 17 hours!!!. She also left early. Our dogs midsection was bloated from lack of opportunity to go to the bathroom. We feel like we've been punched in the gut. We are furious. She lied and didn't do anything we asked. What makes us nervous is that she knows where we live. We are scared of retaliation if we complain. She should never dog sit for anyone again. I feel the dog owners on Rover need to be warned. What should we do?