Maybe she’s financially illiterate and won’t see what a scam your seller finance offer is, but she did have $100k laying around to buy the property, so probably not. 

if there is appreciation, but you wouldn’t sell your current home tax free and buy a neighboring home to rent out, (There by raising your cost basis for additional depreciation and lower capital gains tax.) then it probably doesn’t make a good rental property. . 

Dial in your buy box, then be swift/actionable when ready.

Buy some books and start learning how to manager your property now.

I was living abroad buying/selling real estate mostly land, and some land with structures.

Then, if you can trend over time you'll want to see where the "path of progress" is going/moving and attempt to buy in that path of progress to gain some appreciation in the future.

And where can I buy it? 

You can certainly negotiate some closing costs from the seller on the buy side.

You don't need a conventional bank to buy a property.

If you plan to buy in your hometown, buy a 2-4 unit, and live in one of the units.