Hi, Erin,
I don't know why, but sometimes objects don't behave properly when there's no text in the Normal state. It's as it the object no longer exists to the triggers, even though you can see the object right there...
The fix? Put some text in the Normal state. I created a new oval in the attached version of your file. It's got "..." in the Normal state, but the text is white, so it doesn't show on the slide. (Just using spaces would probably work, too.)
I edited your otherwise fine triggers so they control the new object. The slide now works as intended.