So I assume you had the dialogue with Himari when you've done the Heavenly Husband quest and met her again at the Dealership. 

So what she basically saying was she wanted to have a moment of relaxation but since the public pool is always crowded, she wanted to use your private pool instead. If you accept her request, you can find her wearing a bikini at the Pool ( Not the Public Pool ) on Thursday. After that, you can just go to the Pool any day except Monday to see her again but since this event is RNG, you might have to press the Chat Bubble icon a few times. 😁