Legal Question in Civil Litigation in Texas

This depends. Normally your aunt would have the power to sue, not her daughter since the controversy was between you and your aunt, not your aunt's daughter. However, the court appointed personal representative of an estate of a deceased has the power to sue. If the daughter is the executrix or administratrix of your aunt's estate she has the power to sue on behalf of your aunt's estate. If she is not the executrix or administratrix, she does not have the power. Further the 4 year statute of limitations on applying to administer an estate has passed.

Also it appears that the 4 year statute of limitations on suing on a contract has passed. Finally if there is nothing in writing she can't sue unless the amount in controversy is under $500..