The room it was in however had 12" thick concrete walls, and ceiling and was on a 2' thick concrete slab.

I'll post a pic of one with 12' ceilings. 

Be prepared to pay $75 to an electrician to flip a tripped breaker or change a ceiling light bulb, $75 to a plumber to change a flapper in a toilet or a cartridge in a faucet, $750 to replace a hot water tank, fridge, washer/dryer, $100 to a cable/internet tech to unplug and plug in a modem, the list goes on.

You also get points for the amenities in the house such as ceiling fans, appliances, carpet, microwave, etc.... 

id=1IaAr5B1WeT...Cleanup Job (Low cost fast flip): landscape package in front remove deckremove vines from house clean exterior, fix siding and wood rot, paint neutral beige/gray color clean driveway/weed, clean retaining wall/pavement replace flooring with mid grade flooring bottom level, carpet upstairs replace interior fixtures paint interior white trim, light color beige/gray walls, popcorn ceiling removal new kitchen appliancesRehab options: Replace deck with new one (kind of awkward that high to me) vs Remove and fill in wall or add large window to master.Potential space to move laundry into upstairs bathroom closet vs basement Can maybe get away with toilet/vanity replacement in each bathroomUncertain if painting or replacing cabinets with ikea type is worth itAny in-ceiling lighting will open up codes stuff with electrical since it is out of dateRepave/fix concrete front porch and side porch - replace/paint railingReplace front walkway cement, or remove walkway and replace with right angled walk to driveway (may not provide ROI)Tear down vs paint garage port in back yardWhich do you think provides highest ROI? 

But let's say she had shoved furniture into the attic, on top of the water heater pipes, that eventually leaked through the ceiling & created a repair that cost $500.

For example, when renovating our master bathroom, we decided to install ceiling lighting in the bedroom, which not only added much needed light, but also created an accent wall that makes our bedroom feel significantly more polished.

If you are a ultra conservative very low risk tolerant investor you could pay down a income property mortgage but that is obviously going to reduce your return on your investment to a ceiling of the prevailing mortgage rates.

Your pictures show the sheetrock has fallen off the ceiling.

Did the previous tenant damage the walls and ceilings, or where those pictures from during the tear down?