There are jurisdictions that define tenancy based on the amount of days that someone has stayed on your property, irrespective of a lease or payments. OP should contact a lawyer to ensure that this is not a tenancy situation. If it is deemed to be a Tenancy At Will, then a 30 day eviction notice is the quickest. OP should not dispose of any items owned by their sister, nor change the locks without a separate compelling reason, at least until they are able to get a consultation from a lawyer.