Focusing on what other people are doing is always a problem and I think what needs to be worked on here is that your DD has achieved NC L5 (roughly 50% of pupils achieve this or higher in England in English/ Maths - www.theguardian.com/news/datablog/2013/sep/19/sats-results-key-stage-two - data tables bottom of article).
It's a good result and the higher up that scale she gets the better.
First off ensure your DD understands that the government target for end of KS3 (so end Y9) is NC L5 or NC L6 - so she's already working 3 years ahead of herself - that's quite an achievement.
So rather than worry about X is working at what ever sub-level of 'NC L6' - why not encourage her to focus on improving to the next sub-level of NC Level 5 or if she's working at 5a - making that transition (and transitions between NC Levels are always harder than within I suspect).
So set herself her own personal target and work toward it - don't worry about the other guys.
At home you can help by:
improving the quality of the fiction your DD is reading and maybe discussing things like plot/ author's style/ literary devices (foreshadowing/ onomotopeia/ alliteration/ simile/ metaphor/ etc...)
Work on vocabulary - have your DC read to you and pick them up on words you suspect they're reading but don't know the meaning of. Talk about multiple meanings of words.
If spelling and grammar is her thing - work on this in prep for the SPAG component of the English KS2 SATs.
Maths - well it depends. If the school has regular homework and it's challenging that may be sufficient. But consider playing video games (many free games on Woodlands Junior School Maths Zone: resources.woodlands-junior.kent.sch.uk/maths/index.html) to firm up skills and improve speed of calculation/ speed of multiplication fact recall.
USE BBC Bitesize KS2 games to revise for SATs/ improve skills: www.bbc.co.uk/bitesize/ks2/ - use the games in areas of particular weakness to improve ability
If there's a weak spot - really work on that. Maybe it's division or spelling - but if that's the thing holding your DC back - maybe put in a bit of effort (10 - 15 minutes each week on it - trying to improve).
There are all sorts of fantastic resources on Woodlands Junior School: resources.woodlands-junior.kent.sch.uk/ - especially the maths and literacy zones.
Finally - if your child isn't getting SATs materials from the school which reach into NC L6 (the next step) - then consider borrowing or purchasing workbooks that include NC L6 questions/ concepts. I suspect behind the scenes the children working at NC L6 are doing more at home (have been tutored for 11+ either by tutors or DIY by parents) so perhaps for a few months - because it's important to your DC - why not support her in trying to reach whatever goal she sets herself. (Just ensure it's a reasonable goal - i.e. if she's assessed as working Nc L5c in maths right now getting to NC L6 (improving by 3 sub-levels in one year) is a big ask but working to a strong NC L5b (which should ensure NC L5 on KS2 SATs) is worth it).
HTH