I asked my friend if she was ready to get married. She replied,
I am still getting used to the idea of having to get married.
What does this mean? What does 'having to get married here' mean? Does it mean she is getting used to the idea of getting married? Or does it mean she is getting used to the idea that she has to get married? Is there a difference between the two sentences?
Depending on the culture she is from, there may be things that she wants to do, that she cannot, without getting married. Examples are:
Perhaps when she was younger she innocently thought all these things were possible to her without having to marry. Now she is older she realizes that she "has" to marry to achieve them.
Does it mean she is getting used to the idea of getting married?
Not necessarily. The phrase used suggests that she is getting used to having to marry to do certain things.
Is there a difference between the two sentences?
Yes there is. One is considering the requirement to marry in order to do things. The other is considering an imminent marriage.
The lady in question might never marry, conceivably. She might tell her friends "I never realized I had to marry to do X. I didn't want to marry, so therefore I can't do X.".
Of course, this is all dependent on where you live. In some cultures you can do many things without being married.
"Having to get married" means that there is someone or something that forces her to get married. "I am still getting used to the idea" means she doesn't agree to get married right now, but will in her own opinion, agree some time in the future.
She is likely communicating that for whatever reason, she feels forced into her marriage.
Specifically, she is saying that she is still getting used to marriage being a requirement, at least at the present time, without taking into account the realities of marriage in her specific case.
It's a fairly abstract distinction, but possibly phrased this way to avoid making a comment or implication regarding her fiancee.
What does the sentence say?
It says:
I am still getting used to the idea of having to get married.
Therefore, it does not mean "she is getting used to the idea of getting married."
It means "she is getting used to the idea that she has to get married."
Has to (third person singular) and have to (used for other persons and number) expresse obilgation.
So the sentence means
I am still getting used to the idea of being under the obligation to get married.
It could be something as simple as the place where the marriage ceremony (wedding) will take place is available only on Tuesdays:
I am still getting used to the idea of having to (being under the obligation to) get married on a Tuesday when all my life I have dreamed of getting married on a Saturday.
