My kids "wrote" books that they could then read.
So if you want "at" words, have your child think of words that have the "at" sound in them, then write a story using those words, and illustrate it. Your story will combine words your child can read with words your child can speak. So, the cat sat on a mat. Why would it do that? It wanted to chat. But that mat wouldn't chat.... Those sorts of things. Then you have a book your child can read. My kids are in high school and STILL won't throw away those books they wrote when they were little. Some are hilarious.
I love this idea!. I suspect she would get a kick out of it ( at least until DD10 makes a bit to take over the activity, but that's another issue.)
I will also look in to the other reader serries. DD10 likes Miss Rhonda's readers, but DD5 isn't quite there yet.