Whether she chooses to revise for the exam or not is up to you and her. However, she will still need to sit the exam. How will she feel in the exam and when the results come out if she hasn't revised at all? The literature skills will also be relevant in language.
May not be as easy as you think drop a subject at GCSE. Unless she is already in a low set for English, some of which may not do literature ( I don't know if that is the case or not), what will she do in the English lesson when the teacher is covering literature? She still needs to be in a lesson, supervised and doing something productive.
From experience schools often give information on where pupils can gain guidance. Our school did a bulk order of gcp guides - parents could choose whether to order them (they were discounted to the normal price, I assume because it was a bulk order and there were 2 different books ordered).
There is lots of guidance online such as bbc bitesize.
There are lots of revision guides you can buy. (Maybe look online and see if you can view inside the book) or take dd to a bookshop so she can see what the book is like inside before buying).
We are in Wales and have also been provided withlinks to gcse guidance on the wjec website.
If maths is also a struggle have the school suggested any resources to use? Our school stopped using sparx and went back to mathswatch. They were given a list of topics, and the codes to work through. They also suggested to use the website maths diy. There are booklets to download with exam style questions, and copies with the answers. They gave been doing revision in school in preparation for the exam.
We have the gcp maths books. One of the science teachers suggested getting the science one. I ordered maths at the same time. The science one has been used the most.
Schools will have different ways of organising mocks, because different things work for their circumstances. Our school did a week of year 11 mocks, followed by a week of year 10 mocks in Feb. I know other schools that are doing year 10 mocks after the gcses have ended.
Doing them all in one week meant a morning and afternoon exam each day which felt harsh.
We are in Wales and things are done a bit differently. There are also syllabus changes some introduced for the current year 10, and others over the next few years. The year 10 in our school have currently done an English exam, maths exam and one out of the three science, with the other two being this week and next week. They have complete the non exam assessment for one of the English modules, and are due to start the next nea next week. Lang and literature is now combined into one double award. Not sure if all schools do the maths and English at the end of year 10, but the science being done that way is the norm.
Not sure what the main subject is, and why she has so much coursework to do that stops her revising for core subjects. Is she behind in that and if so is there a reason? What about any other subjects. Depending on how schools organise things there will normally be around 3 options, so she will have more thsn obe, on top of English, maths and science.
I would try and get her to do something in the way of revision for the literature, even if it isn't as much as for example the maths.