Enter her [single] name in the surname field and leave the given name field blank. I guess, this is the correct way for entering single names.
Check this:
http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=014&top=4
And this:
"Where it is determined that the individual’s name cannot be divided into two parts, the name (either the family name or given name), as it appears on the document used to establish it, will be defined as the primary identifier and will be recorded in the family name field in CIC’s system of record.
For example, if a client’s travel document displays the name George in the given name field and the family name field is blank, George becomes the primary identifier and will be recorded in the family name field. The given name field will be left blank in CIC’s system of record.
This is consistent with ICAO guidelines and will facilitate future name searches."
http://www.cic.gc.ca/english/resources/tools/id/name/gcms.asp