If my aunt is executor and she sold the rental units to herself with an appraisal I did not agree with, is there a statute of limitations on this?

There is some additional information we need to know. The estate would have to go through probate for title to legally change. If there has been no probate, there can be no sale, as an executor's powers are very limited. In probate, an administrator can then sell off portions of the estate, etc. No one handling an estate can sell any part to themselves [unless perhaps they are the only beneficiary]. Fraud and conversion of assets have three year statute of limitations; the period for fraud does not start until you knew or reasonably should have known of the misdeed.