She will be joined by her 11-year-old terrier boyfriend, Barney.
The Home Secretary admitted that he will miss Lucy.
Workaholic
He said: "She was not only a great aid to mobility but also a companion."
Sadie's trainer says she'll be a great guide dog and that she's a "workaholic".
She said: "She's very outgoing, she is inquisitive but not fazed by anything and that reminded me of Lucy at that stage of her life."