My friend is working on a relationship advice blog, any ideas on how she could solicit some more questions?

Enlist a few “gurus” who are willing to ask questions, give good answers.

Well making her blog more popular will lead to more people submitting questions. One good way to do this is to participate in other forums and add the link to her profile. One bad way to do this is to spam communities with her site address. She could also poll her friends and see what relationship questions they have, and answer them on the blog.