A: You can sue anyone for any reason. Your real question is, "will I be successful?"
That question cannot be answered without looking at the evidence supporting your allegations and the relationship with your aunt. If you are a disabled adult, as defined by your state's law, and your aunt was your guardian or conservator, then it is possible that a rebuttable presumption would arise. That means, it would be assumed that your aunt breached her fiduciary duties to you and it is presumed that fraud and undue influence came into play. The burden would be on her to rebut the presumption. Your case would become much stronger.
A: After the sale, did you continue living there and paying the lease amount? It's difficult to expand on my answer without reading the agreement (it cannot be oral). Assuming the agreement is what you say, you might consider recording a Lis Pendens on the property. That will get everyone's attention, I can assure you. Probably also consider a quiet title action. None of that advice is necessarily relevant; it depends on what the agreement says.
