I have seen her near the 50's Prime time also in the Hollywood Studios. You can try for the Princess Storybook breakfast in Norway. Make sure you call 180 days in advance 1-407-939-3463. The characters are subject to change there though.
We have only seen her once at the Norway breakfast. Last October we saw her and Mushu at the China pavilion at EPCOT. They have a sign out that she appears periodically there. I think most of the countries do this as well.
Mulan is my oldest daughters favorite so we usually have to hunt her down.