Hello everyone

I am going to a concert on the 1st of may, next saturday. My daughter is 6 mths old and I am breast feeding her. I have to travel 3 hrs to the concert, so all up, I will be gone about 10 hours.
I can't take her with me but my Nan is looking after her. It is the first time I will have left her.

No one has fed her before. I have trouble expressing. I have a hand pump but seems to take forever to express and hurts my thumb. Can't afford electric pump.

Have given her 3 bottles previoulsy, month or so ago, with formula for her 10 pm feed. BUT now won't take bottle, tried different teats. No go.
Was gunna try to express at least one breast feed, but leave formula for other 2 feeds.
Will this b okay??? What if she doesn't take any milk while I am away???
She takes a little farex.
Please HELP ASAP thanks