Brother’s girlfriend?

Hi all, wondering your advice on this decision I’ve been playing around with. My fiancé and I are getting married 8/14/21 (less than three weeks!) and our RSVPs were due back on 7/3. A week or so after, my brother (age 21) met a girl and has been on three dates with her. She has only met my dad so far. My brother is also officiating and knows a lot of my fiancé’s friends, so I’m nervous he would be babysitting a girl who doesn’t know anyone yet. Our guest list is small at 70 people (though I still wanted smaller). The seating chart actually worked out perfectly and adding her would move things around again, likely adding an extra table and we already submitted our rentals. Regardless, should she be invited? I thought a nice compromise could be inviting her for the post-dinner portion, but really feel uncomfortable about her meeting all of our family for the first time that night.