Last year, one of my friends received a competitive PhD offer (including a full-time research assistant position) from a highly prestigious university in Canada, however her request for Study Visa was rejected because of some Social Tie issues. This year, she has a plan to apply for universities in Europe and Australia. Is it worth mentioning her last year offer in her emails to the potential advisors or put it in her CV in order to increase her chance of acceptance? Roughly speaking, the acceptance in the aforesaid Canadian university is considered harder than the European and Australian universities she wants to apply.
I just don't see that information as appropriate... it doesn't belong in a CV or the application. It could be appropriate for a letter of reference to mention it, though.