I was afraid that a pro would either use harmful chemicals that would hurt the pets or that they'd simply be unable to seal the building to keep mice out in the future.

It is not worth the energy and expense to try to enforce the lease, the only leverage you have is harming their credit, which they don't care about right after a home purchase. 

I told the tenant that I would need to call this property uninhabitable (since she had screamed at me about how the mold and bacteria from the sewage water can harm herself and her child) and asked her to find herself alternate accommodations.

We disclose that you are "out in nature" and wildlife may be evident. 

They will need to be interested in basically being a landlord till the tenant buyer gets a bank loan.ANOTHER area new folks get wrong and harms the tenant buyer is the option fee is not handled or contracted correctly for the eventual financing bank to include the option fee paid to be included in the down payment. 

We don’t know any PMCs to recommend in the area mentioned, but since selecting the wrong PMC is usually more harmful than selecting a bad tenant, you might want to read our series about “How to Screen a PMC Better than a Tenant”:https://www.biggerpockets.com/member-blogs/3094/91877-how-to-screen-a-pmc-better-than-a-tenant-part-1-services-and-processesWe recommend you get management contracts from several PMCs and compare the services they cover and, more importantly, what they each DO NOT cover.

We don’t know any PMCs to recommend in the area mentioned, but since selecting the wrong PMC is usually more harmful than selecting a bad tenant, you might want to read our series about “How to Screen a PMC Better than a Tenant”:https://www.biggerpockets.com/member-blogs/3094/91877-how-to-screen-a-pmc-better-than-a-tenant-part-1-services-and-processesWe recommend you get management contracts from several PMCs and compare the services they cover and, more importantly, what they each DO NOT cover.

She takes some of the money she set aside for a down payment and closing costs and uses that to pay off the credit card.Helpful or Harmful?

If there are errors in the report and you can't get resoluation with the appraiser or lender and feel you have been harmed as a last resort you can submitt the report to the appraisers board for review.

That being said, if you're a math guy and like numbers, there's no harm in running them.