I can see Missy Peregrym on the cast list; she is credited for 13 episodes. On the cast page, the people ordered by their number of credits, so people who are credited for every episodes are at the top of the list.

You can see Peregrym on the cast list, because I added here to Season 3. Why is she not in the cast list, when she is only in guest cast in some episodes ? Others are visible with a much fewer guest cast count.

There are some glitches when it comes to tv credits for a person, particularly when the credits are in both the guest cast area and the season regular area. I removed her from the season regular page for season 3, since she is not in every episode. I'm re-entering her credits on each episode, seems to have fixed the issue of her not appearing in the cast page.