I'm such a cynic....I'm just wondering, would an intern have the authority to make such a decision? What department is the internship under?
If it's Purchasing or Buyer, I would put Copyright on everything and spend the money to protect your original designs through the uspto.gov office. Copyright fees are not that much and you don't need a lawyer to acquire them.
If the internship is through Design, I would be careful.
Please keep in mind that I have never had anything like this happen to me or to anyone I know! It sounds like a wonderful opportunity! But it seems to me that a very large retailer is not going to rely on you to provide their product...they will probably desire a larger quantity than you can provide in the specified time. I would suspect that they would prefer to buy the rights to your design so that they can use their current manufacturers. If that's the case, you need to do some research on how that process is done and what price range design rights are normally sold. If I understand things correctly, if you sell those rights, then it is no longer yours and you would not be able to make and sell that design yourself...you would no longer own the right to it!
Just some food for thought. I am a half-empty glass kinda girl. LOL Always suspicious so overlook me but DO be careful and try to find out exactly what it is that you are getting into.
Now, to google 'digital trash can!'