Claimed residency in the Cayman Islands for tax purposes. Constitution has a US residency requirement that she cannot meet until sometime in 2021 – thus her "no interest in running" schtick. If she DID attempt to run, her tax dodging would become the immediate focus. This would not only crap on the immediate attempt, but also echo on future attempts. She probably hasn't actually ruled it out but it's just a "not at this time" thing.
The Democrats need to step lightly around DJTs taxes, because if they are successful with his, we will have no problem seeing hers.