I hope you are getting paid well for an 8 hour stint!
That booking would be a struggle for me, and I was brought up during that era!
My advice:
If she is that fussy, get a play list guide from her, make her do the work.
I'd have thought anything dancable from the 60s upwards to the 80s would be acceptable though and after the first couple of hours they won't care much anyhow. Remember, although she is paying you, there are going to be a lot of other people there of a similar age who may not agree with her choice. Bung in the odd 'other' type of track and see how it goes.
Maybe sandwitch the genre she specifies between disco classics, creating several sixties sessions.
Good luck.......