past continuous for a short action

Question

Things had not been the same between Julie and her fiance, David, since he accepted a job in Paris. They had known each other for almost five years, and in that time, they had never argued much. Lately, though, their relationship had become stormy.They seemed to be finding fault with each other and disagreeing about everything. For the first time, she was starting to wonder if she was ready for marriage.

Why was starting and not started? Is it because of the first times which means she did it after(but we can't call that a start anymore) . Starting is a short action that does not go with past continuous.

Answer 1

It is quite common for the progressive construction to be employed in order to "recategorize" a verb which ordinarily has one sort of aspect into a different aspect.

For instance, stative verbs are not ordinarily cast in the progressive, but may be if the speaker wants us to view the state expressed as subject to change over time:

I'm seeing more and more of him these days.
She was now loving him less than she had before.

In the same way, start or finish, which ordinarily refer only to the moments at which an action is set in motion or completed, may be recategorized as gradual processes.

He's been finishing his novel for three years now.
We're only starting to get a handle on the problem.

Answer 2

The past continuous is used to describe an action lasting for some time or serving as a background for other events.

We often use the past continuous and the past simple in the same sentence. The past continuous describes a background action or event in the past; the past simple describes a shorter action or event that happened for a longer action, or which interrupted it.

So saying she was starting is simple used as a background.