lifelong: She is a lifelong member of the Labour party.

[loviii]

Good day!

Two examples and a definition are from dictionary.cambridge.org:
lifelong - lasting for the whole of a person's life:

a lifelong habit
It's understood that we don't state that this habit will be in the future, we say only about the past.

She was a lifelong member of the Labour party.
Suppose she is still alive now and in order to understand it clearly, replace "was" with "is":

She is a lifelong member of the Labour party.
What will it mean?:
(1) From the present point of time we can state that she is a member of the Labour party all or big part of her life.
(2) The party inscribed her in a special list that entitles her to remain a member of this party for the rest of her life.

Thanks!

 

[User With No Name]

(1) is how I understand it.

She has been a member of the Labour party all her life (up to this point, and she presumably still is a member).

Regarding (2), I suspect you are thinking about "lifetime." A "lifetime" member of an organization is someone who has committed to being a member for the rest of his or her life. (Typically by paying a large one-time amount of money, rather than annual membership dues.)