If I am going to prepare my child for testing, how often can I give her sample questions? How much time should we spend on it each day? Should I stop working with her closer to the test so the material is fresher when she’s actually tested.

This depends from child to child. The bottom line is that you want your child to have fun while learning.  Therefore, if you sense that your child is starting to suffer from “overload” and seems not to enjoy the games as much as he/she may previously have, you should definitely consider giving him/her a break before the big day.  On the other hand, if you and your child are having a great time together, then why not continue the fun games?