DOES THE LETTER OF INVITATION NEED TO BE NOTARIZED?

I WANT TO INVITE MY CHINESE STUDENT'S MOTHER TO COME HERE TO PEI FOR A VISIT. WHILE HERE SHE WILL VISIT PEI AND MAYBE OTHER CANADIAN PROVINCES DURING A THREE OR MAYBE FOUR WEEK PERIOD. I WANT TO SEND HER A LETTER OF INVITATION. SHE WANTED TO COME FOR HER DAUGHTER'S GRADUATION FROM UPEI BUT WAS UNABLE TO FINALIZE THE VISA IN TIME DUE TO LANGUAGE CONSTRAINTS. HER DAUGHTER IS RETURNING TO CHINA FOR SUMMER VACATION AND WILL ASSIST HER IN MAKING APPLICATION FOR TEMPORARY RESIDENT VISA. DAUGHTER IS HERE FOR ONE MORE YEAR - ATTENDING UNIVERSITY OF WINDSOR FOR MASTERS IN ONTARIO.