You have the option to use, or not to use, the article there. "work-life balance" often appears without the article, in which case it is presented as a state, like equilibrium, which needs no article. With the article, it is a kind of balance. What kind of balance? a work-life balance.
The article establishes (or relies upon) the idea that there is more than one kind of balance. For example, saving-spending balance, healthy foods/party foods balance, or even different kinds of work-life balance: the amount of time spent not working that one person needs might be more or less than the amount of time spent not working that another person needs.
In the same way we can use equilibrium with or without an article.
Let's say a person is standing on one foot and leaning in a certain direction, and in order not to topple over, they extend an arm in the opposite direction of their leaning, and they put their free leg also in a certain position. We could say "She has found equilibrium" to mean that she is now balanced. Or we could say that "She has found an equilibrium" to mean that she has found a particular way of achieving equilibrium, as there might have been other ways to achieve it, the leg bent in a different way, perhaps, and the arm stuck out even further.