Can my landlord back out of her years lease?

That depends on what the lease says.  Does it allow termination?  If so, on what basis?  Does it provide for what happens in the case of a sale?   Assuming that the lease does not allow termination due to sale, if this was NY (and I suspect things work the same or similarly in IN but you should check with an Indiana lawyer) I would advise you to, ASAP, record your lease as an encumbrance on title with the county clerk.  It will then turn up on any prospective purchser's title search, and should keep anyone from buying until and unless you reach a deal with regard to your lease or it expires.