I bought a mug making kit from the store, and all the markers were dried out! So instead, I used Sharpie. According to the internet, writing on a mug with Sharpie and baking it in the oven for 30 minutes at 350* will seal in the Sharpie.
Here's the finished mug. On one side:
Because she is! And on the other side:
I'm pretty pleased with how it turned out!