While technically your Aunt is not a disqualified party and, therefore, theoretically you could loan your Solo 401k to your aunt so that she can buy a house in Miami, FL, you still need to proceed with caution before proceeding with this transaction.
Keep in mind that you cannot use your Solo 401k funds in an investment whose primary purpose is to benefit another party--whether a total stranger, a friend, or qualified or disqualified relative --rather than your Solo 401k.
In other words, the primary purpose of any Solo 401k investment must be for the growth of the Solo 401k not for your Aunt to purchase real estate in Miami FL with it.
If the IRS deems that a party other than the Solo 401k is receiving an unwarranted benefit, it can rule that your Solo 401k has participated in a prohibited transaction. For example, if you give your aunt an unsecured loan from your Solo 401k with an interest rate of 3% when the market rate for this type of loan is 6.25%, the IRS could deem the transaction prohibited. While you may have good intention to help out a friend or relative, the details of the transaction should not reflect that this was your primary objective over and above participating in a good investment for your Solo 401k.