First, I'd want to know two things: 1) how much acceleration does she need in this area, and 2) what does the typical 4th grade curriculum for LA look like at her school?
I'd want to know those same two things also.
Like Cricket, the elementary schools my children went to didn't have a traditional "Language Arts" curriculum, and among my friends here and across the US what happens in language arts instruction can be very different depending upon the school - so that's my disclaimer re my own personal knowledge lol. Here are the things we've experienced grouped under "Language Arts" - and how it's sorta worked out for our kids:
1) Individual reading and book "reports" (the reports were very open-ended in format). This is so completely up to the child to choose that challenge was never an issue here - our kids read what they want to read and challenge themselves.
2) Group reading - whole class reads a book together. This was beyond boring (during the *reading* out loud part) for my ds - he hated the slowness of it. However - he didn't mind the level of books that were read because by the time he was in 4th/5th grades the books that were chosen were still interesting to him even though he was capable of reading at a much higher level - so he enjoyed the subject matter and the class discussions etc.
3) Grammar - this wasn't taught very much explicitly (from what I can tell) until my ds was in middle school. He was in what's the equivalent of an honors class, and he probably could have learned more quicker and yep, it was boring, but we didn't push for acceleration. He's much more of a science kid and by the time he was in middle school he hit a happy place with getting the appropriate acceleration he needed in math/science (note: we aren't totally there yet either - but it has been much easier at middle school because of the nature of classes being taught separately etc).
4) Writing - my ds has a learning disability that impacted writing in a huge way when he was younger, so we weren't looking for acceleration, we were looking for help! FWIW, his writing took off once he *was* appropriately challenged - so this is an area I'd really *really* advocate for assignments that are up to your child's intellectual level. My ds is never going to be a talented writer (at least I don't think so!) but so much of the frustration he had with early writing has been eased significantly now that he has subjects to write about that are discussed and analyzed at a deeper level of understanding.
More on writing - my older dd is MG, and her strength is creative writing/art/etc. She's not accelerated in language arts, and really doesn't need to be for things like grammar etc - but with her we encourage her to read read read at home (which she loves) and we keep a mom-dd journal where we write to each other back and forth and I use that to push her a bit in her writing - which she loves. We also give her art assignments for "homework". Basically we're informally supplementing at home just by feeding her creative side and having her practice. I think that it will serve her well in preparing her for middle school, where LA levels are grouped.
polarbear
