I think reading is one of the best things she can do, and Antolin is great as it gives both of you a good idea of how much she is understanding. When you enter the name of a book it tells you the grade level but I wouldn't worry about that too much. I think any reading is good reading at this stage. We used Antolin a lot when my daughter was in the 2nd class (she's now in the 4th) and it really helped to build her confidence.
You could also try the Lük and Minilük puzzle as well (http://de.wikipedia.org/wiki/LÜK
You can buy the actual puzzle device and also do it as an app, I think. There are lots of different puzzle books covering all aspects of German language as well as maths etc, and you should be able to find one specifically for the cases or that at least includes it. It can be expensive but try second-hand, too, such as Ricardo. My daughter's class also used this quite often in the 2nd class, I think, so ask your daughter's teacher if she can find some for you.
Otherwise, my daughter's teacher gave her a book to help her understand the different articles, and therefore by default the different cases, too. It was from the Kantonaler Lehrmittelverlag St Gallen (http://www.lehrmittelverlag.ch/Categ...=Fachbereich_1
) so that might be useful, too.
There's also a Zürich one (http://www.lehrmittelverlag-zuerich....H/Default.aspx
) and my daughter has used this online for maths, and I'm assuming it might have some good language stuff as well.
You could also try something like Duolingo: https://www.duolingo.com
and I'm sure there must be lots of other apps out there.