My question is how do I go about properly putting the guest out and can I ban/prevent this guest from coming to the property since the length of her stay was a violation of the lease? 

I know if nothing related to COVID That prevents a landlord from raising the rent.

Fannie / Freddie & FHA all allow this time frame, however some lenders do have overlays that will prevent them from allowing the 1 year rule.

Sometimes zoning can prevent use as a dwelling, other times no problem.

How do I enforce appointment times and prevent tenants getting harassed?

They will deal with the clogged toilet calls, etc...

They also make locking caps for the high side low side ports to prevent the refrigerant from being stolen.

Now you could try to prevent them being an employee but making them sign an independent contractor agreement of sorts.

You would be looking at a short sale, and most lenders will have an arms length agreement involved preventing the sale of the home to a family member (Unless it's a reverse mortgage).

Lifelong, systemic lack of access to primary healthcare and nutrition, as well as environmental factors like pollution, can contribute to a higher likelihood of illness and death from the virus, according to the Center for Disease Control and Prevention.