Music festival

It sounds as if your event is both planned and paid for and your daughter has since asked you to babysit. If that’s the case why not explain to your daughter and offer to the take the baby if she’s happy for you to do so and you honestly believe you could cope with unexpected baby issues. If that particular evening is vital for your daughter is there an alternative babysitter? I’m wondering how your relationship is. Are you worried about your daughters reaction if you say ‘no’ to her request? It’s certainly not something to consider without your daughters blessing so first step is a conversation with her. You can’t decide until then.

What if she cries and won't be pacified?
You would have to take her out or risk her spoiling the event for others as well as yourself.
Is there no-one else who can babysit?
And whose event was planned first?

If you are already booked to go out, why can't you say sorry
we are out, so not on this time.

As Luckygirl says ask DD, but personally not something I would do.

We used to lug our little lasses all over the place from a very young age.

What does your DD think? - I guess that is the crux of the matter. And what is she going to that is so important that you must babysit at that moment?

I would take a baby of my own, but probably not a GC so young.