While you probably “could”, I would recommend against it, especially if it’s just for an event/something one off.
Opening a joint account with someone links you both financially, impacting both your credit files, not just within Monzo, but for all credit. So by setting up a joint account between you and your daughter, loan applications, credit cards, mortgages, etc, will impact you both and providers will see the association when applying.
If this is solely for the purpose of event planning, and you both need to make payments towards it, then maybe look into using the “Shared Tab” functionality instead to see if this suits your needs.
You could also look at adding your daughter as a 2nd card holder on a Credit Card but do check with the providers to see if:
a) you can add someone not at your address
b) they report the 2nd card holder to credit agencies
as it differs from provider to provider. (Monzo doesn’t allow 2nd card holders for Flex), but do check to see if it suits your needs first, and the implications of having someone use YOUR credit.
It feels like they’re only working on minor periperhal features tbh. We will get some drop-feed of “here’s something that now works that you don’t even use on your main account because it was easy for us to fix”. Whereas custom categories (previously a most-voted-for topic, back in its day), and virtual cards will be kicked into the long grass forever.