Replying to Me and my girlfriend...

We are going out to NYC on saturday and she'd be picking me up at 5 oclock... so I said why not just have a sleepover friday night. I'm 15. so I'm young and we've been going out for awhile... but she ended up asking her mom, whos normally tight about that stuff, but she said yes surprisingly. Her mom called my mom and asked her if it was okay. My mom doesnt feel comfortable. I told her we'd sleep in different rooms and shit and she still wont allow it. What can i say to her? and im being serious guys haha.