DD got an A* in all her sciences and has found the jump to A level very hard. Her chemistry grades started off at C, crept up to a B and she is now working at an A. With A levels only three months away at least she is going in the right direction. My niece found that it all clicked in year 13 as well.
DD is lucky that one of her chemistry teachers is a brilliant teacher and does a drop in after school once a week. She has found these drop in sessions very useful.
I am not sure that chemistry does ever " click" with some people.
I have a degree in Chemistry. I found other subjects difficult. History and languages were not my thing. I have two kids, for one Chemistry was easy, and he "clicked", sailed through A level without having to study. My DD struggled with the subject, although she finds other subjects easy.
Our brains are all wired differently. It doesn't make for cleverness, just difference.
There is a thread called "Last term of Year 13. Gulp" in Further Education with Mums of DCs who have just done A level Chemistry - you'd be very welcome to post on there and ask about their experience.
Chemistry teacher here. I think it is important for kids to read through their notes and process the new content after every lesson. Sometimes just a read through is enough, other times more active work to make sure it is embedded. Chemistry is like a language you need to know and understand prior learning to understand another topic. It constantly builds on itself. The course is very content heavy so a teacher often doesn't have to re-teach essential prior learning before teaching the new content.
I'd recommend going to YouTube and watching "fuse school" or Khan academy tutorials to help. Also when your dd starts a new topic she could ask the teacher what she could look up before to help her get it in class. Going over her GCSE revision books would also help. Hell even stuff covered in year 7 and 8 is relevant (but probably forgotten by most students).