In 2013, Obama invited all of his living predecessors to accompany him to Mandela's funeral, & all but Poppy Bush (due to his health) did, so given who she is, I imagine they're all invited, with Clinton, W., & Obama all accepting & attending with Biden on AF1, Carter declining due to his health, & Trump presumably declining so that he doesn't have to be near Biden, although I could also see him weirdly but genuinely wanting to actually go since.. well, I mean, c'mon; she was The Queen.
Even Donald lowers his Ego before the Queen.