She mentioned a commercial policy or getting a second umbrella policy under another carrier? 

In a market where rents are depressed, the RC will often be significantly higher than the ACV.The problem with ACV is that, on a partial loss, the claim, under an ACV basis, has a deduction for depreciation.You will have to kick in for the deductible and the depreciation.If your Rental is in good shape, updated systems, well maintained, etc. the rates from some companies with onlyRC may be equivalent to others that will only do ACV.I just wrote one in CT that one of our carriers for $400,000 RC was $100 less than the next best rate which was based on $110,000 ACV for the same property.There are many endorsements that are available on the Homeowners policy.

Carriers have their sweet spots.

Major carrier lease rates can be $2k-6k per month. 

Also, you're going to need professional guidance when it comes to asbestos, so hence best to involve your carrier early on in the process. 

-If you had a landlord policy, but did not have this coverage, than your insurance agent made a mistake and you could claim this loss under his E&O-If you had it insured as a Homeowners policy (owner occupied), and had it rented, the insurance carrier could have denied the claim.Did you have it insured any other way?

Each carriers policy can vary a little, so double check with your agent that the demolition is covered. 

This is why insurance carriers do not like vacant properties because no one is there to stop something like a simple water leak. 

As far a the instance is concerned many of the insurance carriers offer a discount when combining home and auto insurance.

You will have to go after their insurance carrier to cover the claim.