@Laura2592 It's a Trojan Horse guest. They book under the pretext of a normal reservation of an appropriate size, knowing full well that they intend to use the home for different purposes and bring more people in. Sometimes, when it's getting close to the date of their stay - perhaps too close to get re-booked - they'll ask for a little leeway. Just a couple close friends or family members, of course, only for a couple hours, etc. And inevitably, it turns out to be a much larger number of people, a different kind of occasion, a longer duration.
Perhaps the guest genuinely is a bride-to-be, but it's interesting that she didn't mention the stylist and photographer, and those additional friends who just "randomly" turn up at the last minute. An honest guest would have initiated that discussion before placing the booking, rather than putting you on the spot at this late stage; I wouldn't trust this one for a minute.
Anyway, the other members of her group are presumably either residing or staying in other accommodation close to the wedding venue, so refusing their request wouldn't result in it being impossible for the bridal party to get ready. Perhaps they'd have to settle for a less Instagram-worthy backdrop for getting their hair done, but that's a First World Problem if there ever was one.