Alison Weir in her book on Mary Boleyn asks whether the portrait we'd all assumed was of Mary was in fact Frances Brandon.  Lady Margaret Douglas, another of Henry's nieces was another name she put forward.  This, of course was based on the fact that the sitter is wearing ermine which Weir says only royalty were allowed to wear but there are portraits of other non-royal ladies wearing the fur so i don't know if Weir is quite right on that point.  She also says at one point the portrait of Mary was mis-identified in the past as being one of Anne – that I can go along with as the identifications of Tudor people is such a mine field!  Although I don't think it is Anne, the sitters facial features have very little in common with the NPG/Hever versions of Anne.

What is known about that portrait of Mary is that it dates from at least two hundred years after she lived so if its supposed to be her or not no one can really say.  I like that Weir has raised questions about because there's a very good chance it may not be of Mary at all.  Gah, sometimes Tudor portraiture makes my had hurt – I'll never understand why they couldn't just put the persons name on it!!!!!!