Hi Glen,
The getParent function will not give you the parent Client - it will only give you the parent entity to a particular attribute on the form. There is no Xrm.Page.data.entity.getParent function unfortunately.
You will need to use the REST or SOAP end points to get the client name. I would suggest that you use a web resource to show the information rather than populate a field (unless you need to) - see blogs.msdn.com/.../showing-related-information-in-a-crm-2011-form.aspx
hth