Yes, if she is visiting you in Canada, she can still apply outland. There is no problem with putting her Korean address as her residential address and your Canadian address as her mailing address.
Many people on this forum have stayed in Canada as a visitor while their outland PR was being processed, and have put the Canadian address of their sponsor as their residential address (and their mailing address), even though they were technically just visiting. None of them have reported any problems with this. If she is visiting you for a few months, I would use her Korean address as the residential address, but if she has been there or will have been there for more than 6 months, I would use the Canadian address as her residential address. (But there shouldn't be any problems either way.)
You can always add a note explaining the situation to the form.