Oops sorry I didn't see the fact she's a student.
I would just be honest and say she's visiting a friend, because if she gets interviewed at the border and sticks to her story of tourism, but then cracks and says she's actually visiting a b/f, it could raise some red flags. Also, CIC might feel she has a poor purpose of visit because why would a student in another country, travel to Canada alone, where she doesn't know anybody there or have any famly, for tourism when she has studies to attend to? Traveling to visit a b/f for Christmas would seem to be a better purpose of visit.
Be aware that it might be hard for her to get a visitor visa, because she does not have some form of permanent status in Singapore (not a PR or citizen there, but just a student), and this does unfortunately, sometimes causes people to be refused a visa.
