Hello @stephenm.schwartz
I have moved your question to a new thread, since it was not related to the topic of the original discussion.
If you both (you and your granddaughter) have both created an account it is very easy. Click the upper left OGS logo and search for her account’s name. (Also see below). Click on her name and click challenge. A table will pop up that should be pretty self-explanatory. Set the board size, time-settings and so on… If you are not sure about some of the settings leave them at default or ask here 
You can find answeres to other most common questions here: