Any recommendation sight reading material?, Jazz piano grade 5 Options

[chickenfingers]

DD is having difficulty with jazz sight reading. She is doing well with classical grade 5 sight reading, but struggles with the tricky rhythm of jazz grade 5 sight reading. Jazz piano sight reading seems so much harder with the unusual rhythm and pulses, but they also expect a spontaneous improvisation as well with max preparation time of 1 minute.
She is actually doing OK with the improvisation part (her strength) but only if she could get the initial score pulse and rhythm correct. I think she passed her grade 4 jazz sight reading, but not particularly well.
I have the sight reading practice materials for grade 4 & 5, but the problem is she practically memorised them after 1 or 2 practices, and so I ran out of materials for her to practise on.
So I wonder if anyone has any suggestions what would be good material to practise on?

[TSax]

For me, learning to sight read jazz material hasn't been so much about practising lots of sight reading. As you say below, it's the rhythms that are the tricky bit. What's worked for me is working on the rhythms, repeatedly - not just sight reading them, but taking them apart a bar or a phrase at a time, and not necessarily with the instrument. Clapping with a metronome works for me. This works for me because now when I see a particular rhythmic pattern in the music I know how it goes without having to work it out.

There are a couple of study books I know for sax that work in this way (the Lenny Niehaus studies, and "Reading Key Jazz Rhythms" by Fred Lipsius) but I'm afraid I don't know what's available for piano.