I think that this is something that only time will tell. HCB and Vivian Maier are very different photographers. The first has had many years to establish his credentials and it is clear that he is one of history's premier photographers. Perhaps, over time, Vivian Maier's work will also establish her as one of history's great photographers, I really don't know yet. To some degree that will probably depend on how well her work is promoted, and how well it is accepted. Talent certainly plays a part. A strong work ethic that produces a huge body of work is also a positive. A good story doesn't hurt either. But in the final say, continued success in promoting her work will probably be the most important. Right now it appears that the shows of her work have been well attended, it seems the books with her pictures are selling well, her website has a lot of hits, and there continue to be stories presented in the media. If that continues over time, then her name and her pictures will be established with the public. At that point I strongly suspect that she will be considered a great photographer by most, no matter what you or I think.