I was surprised Paola agreed to come on the trip, just her and me.
I was surprised Paola agreed to come on the trip, just me and her.
Both versions sound OK to me. Or is it there a more appropriate one?
To be honest I think the whole sentence is a bit clumsy with either.
I would suggest something along the lines of:
I was surprised Paola had decided to come on the trip, as
it would be just the two of us.
Of course, I could be misreading the meaning of your original sentence – I’m assuming you are surprised because Paola has decided to attend a trip with just yourself?