Send her any required notices (claim against security deposit, etc), change the locks for real this time, turnover the unit, and move on.You should be able to charge her (and claim against her security deposit) for removal, disposal, or storage of her personal items, cleaning, damages, etc.

She told us there was water damage to the floor but it looked ok until three days ago they removed the floor and sent us a picture it was black. 

If they damage the property, leave it dirty, etc, you're not going to have to worry about a few dollars in interest.

The relationships that I built at that mastermind group lead to some pretty awesome deals that have made me hundreds of thousands of dollars.My newest mastermind group is with 4 other investors who are doing things at a big scale and who have followings and influence and who also coach other real estate investors.In other words, I created a couple of the mastermind groups myself and the others I joined or bought into.  

The neighbor who lives there told me that there was a house before on the lot and was fully damaged by fire and the house was demolished leaving only the lot.

With today's current environment (Coronavirus damaging the economy) have I picked the wrong time to become a wholesaler?

I was quoted around $10k JUST to add the piers to reinforce the existing damage- but without additional drainage and re structuring the damage would continue to the crawl space. 

@Paul ZhangI would do your walk through and take photos for your records and then have the tenant do his walk through and document anything that is broken or damaged or that he wants to note for your collective records.

My concern is how will I know the exact condition of the apartments for any damages, problems, etc?

Meaning that they don't have multiple late payments, cause damages to the house, cause unnecessary wear and tear, exceed the occupancy limit, breach the lease in other ways, etc. .