"I want you to live on land as my girlfriend for a week."
"That is not an answer that I was expected. It is posible: I can transform into a human, but I have never been farther from the ocean than the beach."
"I don't know what it's like to live in the ocean, but life on the land can be fun. There's lots to see and do, especially if you've never been here before. I can show you while we get to know each other."
"And at the end of the week?"
"You're a beautiful young lady so I hope you'll want to stay with me. But if you don't want to, I wont stop you."
"Very well, lets go."
She walks out of the water, having transformed into a human again. You follow, getting a wonderful view of her beautiful body. That's when it occurs to you she has no clothes on! You will have to be careful getting home without being spotted by anyone or you will have some awkward explanations to make.