I forgot about Windy Hill - this may be an ideal place for your friend as they show A circuit but also have good lesson horses. Its about 40 minutes from Peterborough. Coach is wonderful. Relaxed and fun - ideal for lessons.
Probably one of the nicer facilities around too: http://www.windyhill.ca/
And I would second Natalie Smith as well, although adding another 15-20 minutes to the drive.