Child listening issue

[CanISpeakToYourManager]

This isn't a 'my kid never listens to me' problem.

When my daughter (nearly 13yo) is listening to ...anything...if she encounters a word or phrase she doesn't understand she loses the thread of the conversation. This keeps happening in science particularly. If she doesn't quite understand what the teacher means, she just sort of blanks out and then finds it very hard to pick up the thread again.

If I'm reading something aloud to her and she doesn't understand a word, the rest of the passage is lost to her.

Is this common? Is this a language processing issue or an attention issue or similar? Is there anything I can do to help her, given that it isn't always appropriate to stop and explain words?

Is this a new thing for her? Does it happen when she is reading, or just with speech?
I think it warrants a trip to the GP.

She's always been like this. It is just starting to be really obviously a problem.

She also regularly says things like, 'Oh, I thought you said xyz [similar but totally different thing that is nonsense in the context]' - I think everyone does that sometimes but she does it really frequently.

I'm wondering about auditory processing.