My sis smamed my frends party invitations

Your best option would be to password/passcode protect your account if your sister has easy access to the console.

I would advise not allowing others access to your account, as you will be held responsible for their actions while on the account.

Have you been banned or suspended? If not, just be sure to avoid any spamming.

And if u where online at the time of being banned or suspended? Xbox will send u a message to your account explaining why with a way to review your case.

I would suggest putting a password on your account and setting her up with a kids account