I struggle with this a lot. I absolutely will never set foot in one of those places again, so that includes funerals. I don't think that's petty; I think it's necessary for my survival. At the same time, I don't think I could ever bring myself to tell my mother that in advance.
My thought has always been that, out of respect for her wishes, we can arrange for her to have a memorial talk at the Hall. However, I fully intend to not arrange for that until after she has had a real funeral at a funeral home. We can make an announcement at the end of her funeral that a memorial talk will be forthcoming and people are welcome to attend that if they'd like to. I also plan to put in her obituary that donations can be directed to one of the charities she actually likes and supports, like the American Diabetes Association or the American Lung Association. And I plan to promote her volunteer work for them, which she does in spite of admonishments from the elders, in her obituary as well.
The reason I wouldn't announce a memorial talk in advance is that I really want active JWs to attend a real funeral. I fear that if her obituary said she's having a funeral as well as a memorial talk, they'd only go to the latter. So I wouldn't approach the elders about a memorial talk until they're already in the door at the funeral and therefore can't steer people away in favor of the other function.
Side note...my mother heard from many people in her Hall (my old one) that they were amazed at the funeral we had for my grandmother, a non-Witness. The eulogies came from me and one of my sisters and were very much all about Grandma. The elder who made a few remarks at my mother's request could only read directly from the obituary (which I wrote) because he had no clue what to say about her as an individual. The difference did not go unnoticed.