Are you using 1997 Formats or the new 2011 Formats Guidelines?
If using the new guidelines, follow print order and treat this as front matter. See section 2.7. If using 1997 Formats, treat this as a p-page and put it after the Table of Contents, if there is one.
In any case, the print order should be carried also in braille, thereby giving the braille reader the same experience as the print reader, encountering the index in an unexpected place.