Don't forget that if the house is worthless and you're just buying the lot, it's not worth what the county says it is. There's some figuring involved regarding what it would cost to build a house to the square footage that would achieve the market average for that area.
But at a minimum you need to figure in the cost of demolition, which I'm guessing would be around $7k to $10k, just looking at the pictures and over-estimating a bit. That demo cost should come off the price of the lot.
Even if you replaced the house with a small thousand sqft at only about $60/ft, that's $60,000. Add in the $10k+ for demo, plans, permits, etc... Now your at an easy $70k, plus the lot and whatever other costs you may have incurred, you're at or over the $100k target. And obviously, no investor is going to all that trouble just to break even or lose money...
Even if it's not a tear down I think she's probably asking too much... Something to think about.