The Dork Diaries. y5 Dd is loving them.
Meg Cabot.
older Jacqueline Wilson books: Girls in Love (& related titles), Dustbin Baby, The Illustrated Mum, Lily Alone, My Sister Jodie, Kiss, Lola Rose (but that is fairly heavy), and younger & funny JW books: Double Act, Tracey Beaker series. Girls series is very funny (can see videos on youtube, too).
Darren Shan books. If they go for horror!
How "struggling", if you're honest?
Calvin & Hobbes, Asterix, Tintin & other graphic novels still go down a treat with my y7 boy, but my y2 not-brilliant-reader child can read them, too.
Sprite Sisters, Jiggy McCue, Indie Kidd (but might seem a bit young?)
There's a book that DD just read, part of a series about 3 Asian sisters in approx y6-y8, dealing with silly situations, quite funny, will look it up if you want.