As a younger female myself, I understand your concern.

These are some strategies I use to insure my own safety:

1. ALWAYS tell someone where you are going and when you will be back. I share my calendar for Rover appointments with someone I trust so they can see the address I will be at and about how long I will be there for. I recommend you do the same. Inform that person that they should contact the authorities if they don't hear from you in a timely manner.

2. Ask if there are any cameras in the bathroom or bedroom where you will be staying. Most of my clients will use cameras but you have a reasonable expectation of privacy in the bedroom or bathroom.

3. Carry pepper spray (if it's legal in your area). Also, some self defense classes couldn't hurt!

4. Trust your instincts. If you get a weird feeling from someone, don't book a stay with them.

If she has officially cancelled the stay then that will depend on your cancellation policy. Rover gives you three cancellation options: Flexible, moderate, and strict. Moderate is the default. You can review your cancellation policy under Services & Rates in the "Preferences" section of your profile

I agree that the most likely explanation is the dog has bonded with the sitter and is feeling protective. I would still recommend a vet trip just to rule out any possible illnesses. Owners should be told immediately and the sitter should take extra precautions to make sure no one is harmed.