It was fully flipped and we offered slightly less than asking.

Then make certain they can offer what you need. 

If a realtor won’t do the deal for $5k you can EASILY get a state legal contract for under $100.

Today I was approached by someone who is offering me around $1800-1900/month to rent the property from me to run a short term / medium term rental out of it, primarily for traveling nurses or other business people.

Is it legal to charge non-refundable pet deposit and monthly pet fee in Wisconsin?

The screening they offer works well. 

I responded to her FSBO ad and made my offer which she happily accepted: a 36 month lease option; I'll bring her mortgage current, (1 month, $800), and continue making the monthly payments; option to purchase price of $88K, (my estimate of value, $100K); and I had the right to buy, sell, sublet, or assign the property at any time during the 36 months.

If you are willing to put down a larger down payment it might make sense with the flexible underwriting they offer, especially if you are going to run it as a MTR. 

We welcome any suggestions or insights you may have Additionally, if anyone has information on the approximate cost of building a duplex and triplex in California, we would greatly appreciate your input.To provide context, neighboring properties in our area offer insights into the local housing market.

Have you received any offers at all?