A minor aside: I don't know anything about the person Penelope, but one key to popular characters is to be relatable. This also applies to the persona one projects. A person with a very popular blog is likely an expert at being relatable - part of that is being an everyman/woman, and sharing the trials and difficulties, the foolishnesses and mistakes that many people can relate to and feel comfortable around. i.e. not being an "expert".

A blog might also include explicit expertise, in the form of a secondary character: a mentor. But that's not the entry point for the reader; it's not who you relate to.