Cousin Uses My Toothbrush, How Do I Stop Her

A listener wants to know how to stop her cousin from using her toothbrush! Do you have some advice for her?

I have to say, I get the BEST emails from you guys!

This one is from Randy, she says (yes she),

Letting family stay over your house can make a person crazy, but what my cousin did was so vile I had to tell you about it . . . Apparently my cousin forgot her toothbrush when she came to stay and instead of running to the store to get one, she just decided to use mine!
What's worse it she's been staying with us for the last three days and I JUST found out about this YESTERDAY! I freaked out, but she doesn't seem to think it's a BIG deal. First off, how can someone do that without throwing up?! and Secondly how do I get her to stop!

I'll be honest I have no advice, maybe this is your million dollar idea! A chance to invent a product to keep people from using your toothbrush?

What would you guys tell her?