How Do I Give Access to Someone Who Was Added to My Tree by Someone Else?

My son created a simple family tree on geni.com many years ago. At that time, both my sister and I were added. Since that time, I have worked to add many others to my tree. My sister has, until recently, just enjoyed seeing the additions as they take place. My sister has received new information about her husband's relatives and would like to add them to the tree; however, she does not have access to do so. Her e-mail address is already in geni.com, but she is still unable to add or change any information. Any ideas of how she can do this short of creating her own tree or having me make changes as she needs them would be helpful.