A bit of both. I think her personality is just so strong and fantastic that she'll never really be in any danger of being lost in an episode. I also don't think she's been overshadowed yet in any of the episodes. Even as a face on a statue she's an important plot point.

I suppose I do prefer an ensemble cast in general to a "Person A and Sidekick B" style of writing, which has been why this character heavy season hasn't upset me, but I truly don't think Donna has been shoved aside yet, and I doubt she ever will be.