I agree with PPs about the fact that it somewhat depends what age/year she is in, and how close she is to achieving GD at present. What has the teacher said?
A goal of giving your DD some extra support in reading/writing is fine, and there’s lots you can do, though I would be inclined not to focus on the Greater Depth aspect. If she enjoys reading/writing, and is happy to spend some extra time on it at home with you, she will be more likely to reach her potential in these areas this year, regardless of whether that’s actually GD.
It’s difficult to advise without knowing her age/year, but for reading I’d suggest to spend plenty of time reading a variety of things with her: school books, choices from the library, modern and traditional stories, poetry, non-fiction, news etc. Encourage her to read aloud, quietly to you, and also ‘speech’ style across the room, with lots of expression. When she encounters unfamiliar words, discuss what they might mean, and then look them up in the dictionary. Ask her to think of other words with similar meanings, and then look in the thesaurus. Give her plenty of opportunities to read by herself, perhaps by going bed earlier, or in the car / waiting room. Always have a book or word puzzles on hand for those little moments.
For SPAG, talk about ‘unusual’ spellings when you come across words. If she has weekly spellings from school, go back through previous ones periodically to ensure words aren’t learned and then forgotten (I always photograph spelling lists for future reference). If she likes doing things online, perhaps look at Squeebles, or IXL for practising grammar.
For writing, encourage her to write shopping lists, thank-you cards, write to her friends (or an imaginary fairy or similar?). The BBC Radio 2 500 words story competition is currently open, which is a great opportunity to get a child writing imaginatively.