Hours after Derek Jeter's ownership group closed on the purchase on the Miami Marlins ... #2's wife, Hannah Jeter, hit the town -- lookin' like $1.2 billion!!!

Hannah was spotted out shopping in Tampa on Monday -- with witnesses saying she hit up a high-end shoe shop and a fancy salon before meeting up with her new MLB owner husband.

Derek reportedly has a 4% ownership stake in the group that bought the Marlins -- but appears to have serious pull when it comes to personnel decisions.

Get it, Jeters.