hi there Richie.. your wife is probably approaching the menopausal age.... so it might be hormonal changes taking place or it might be due to pregnancy as u said... or it might even be due to any other reason.. Usually implantation bleeding is spotting rather than bleeding... if bleeding persists for 5 days it's not pregnancy.. however it would be good to get it checked by a gynaec..
it is more than likely just her hormonal balance actin up a little it happens if she is under stress.