Tearing around the room, spitting out her pill, and glaring at you from under her chair? Sounds like a healthy, normal cat!

Give yourself credit for getting her checked out, and for agreeing to get her spayed at what turned out to be the exact right time. There's no other way you could have known she was ill -- even her blood work was normal, for god's sake. Glad to hear your mom will get the other kitty spayed, and super glad that Pebbles is doing well!