Generally, introverted and conservative girls send text messages saying that they should think things over after rejecting boys. What does this mean?

To think clearly, I personally think that if you like her, she may have a good impression on you. She is afraid that you are just joking or insincere, and she doesn't want to waste time and energy on this matter or you, so she says so. Second, if she doesn't like you, it means that she doesn't think you are on the same level as her. Said it was to make you think clearly about whether you should confess to her.