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

Then make certain they can offer what you need. 

Your offer to purchase should include a requirement that the Seller provide all documentation and agree to sign an estoppel certificate (also called an estoppel form or agreement).

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.

Thank you for the offer.

You'll also receive a lower ranking on Airbnb and other listing sites because you don't offer an amenity that everyone else in the area has. 

Have you received any offers at all?