There is the gigantic_breasts tag, which is supposed to be for breasts larger than the head. They aren't that much bigger than her head, so I'd say huge_breasts is fine. Feel free to correct me if I'm wrong, though.
Has anyone ever considered an "ubertits (or breasts)" tag... seriously, though, I don't understand why this site won't allow pics with chicks whose tits are much, much larger then their heads.