My understanding is that you'll need to tell them if you bring a lawyer because they'll have to have their own there as well. But you aren't required to tell them you're bringing anyone else.
In my first few meetings with our school about my son's dyslexia and 504, I told them I was bringing a dyslexia expert (either the head of the dyslexia tutoring company we used, or my son's dyslexia tutor, who was a former special ed teacher herself), and I think that prompted them to bring in their own district expert. I do believe it resulted in a great 504 because the school wanted to prove that they were doing everything they could. (Which wasn't much, since he didn't qualify for an IEP.)
In your case, I would let them know-- I think it would send the message that you're serious. But I wouldn't give them a lot of details. I think you might just tell them that you're bringing an advocate or expert and that she can't come at 8 a.m., and the suggest some times that do work.
