How was Liz 10 still alive in 5145 when in "The Beast Below" it was 3295

In "The Beast Below", it was established that her aging rate had been radically slowed down (she was not herself aware just how very drastic the slowing had been). By 3295, she'd already been on the throne several centuries, although she remembered only a few decades of that. Since she's hardly aging at all, she's almost immortal.