levelling influence

Recklessly eager to allay suspicion, she perched herself on the arm of his chair and nibbled the cake from his plate, as though to demonstrate the levelling influence of domestic happiness.

I came across the sentence above in a novel written in the 1930's by Ethel Lina White, entitled Step in the Dark.

I wonder what is meant by "levelling" in this context.

We don't have much information about who these people are, but the idea may be that domestic happiness tends to overcome distinctions in social rank.

Making equal.