As far as upgrading your friend's daughter to first is concerned, a lot would depend on the details of the daughter's ticket and on whether space is available. Some economy tickets can be upgraded; others can't.

I would not advise sitting in 9B's seat and then asking if he/she would like to move to 4B. Nor would I ask that the passenger be paged at the gate. Perhaps a flight attendant could serve as an intermediary.