Seriously, you might want to rethink your travel agent. I understand that she may have to recommend places that will pay her a commission, but you want a travel agent to facilitate what you want, not tell you to want something different.
That said, there is some sense to doing a week on the beach then a week on the cliffs at BCC, and Grand Pineapple as others have said puts you in the middle of things while providing support for the first timer in Negril while you learn the runnings. Riu and the other big AIs at (or past) the north end of the beach I would not especially recommend; if you're there, you might as well be in Mo Bay and save the drive to Negril. We love the beach, but good friends have stayed at BCC and it's a very impressive place - just not on the beach.
You can read up on Grand Pineapple quite a bit here, and they have their own Web site so you can see what they offer. Don't worry too much about needing your AI to provide all the activities you want, because there are plenty of options for everything, and the AI may well only be subcontracting for the activities anyway.