[onetwo_threefour]

^ Almost right, except the part about the agreement to the contrary and the confusing term 'specific fixed term tenancy'. All fixed term tenancies are specific, that's what makes them a fixed term, therefore section 15 applies to all fixed term tenancies. Notwithstanding means 'despite' or 'in spite of in more common language. That means you can't make an agreement that requires notice to terminate a fixed term tenancy, it would be contrary to the act and the notice requirement would be void. This section is one of many in the act that restrict what kind of language you can put in a lease as a matter of 'consumer protection.' If the OPs sister had a term in a fixed term lease for one year that said the lease could be terminated by the landlord on X month's notice if the landlord wants to sell, that term would be void. This is just further support for a tenant in the position of the OP's sister, even if there is a termination by notice clause it would be invalid.

Your example of converting into a periodic tenancy is a renewal provision, not related to notice to terminate the fixed tenancy. The fixed tenancy ends on the date originally specified and a new periodic tenancy starts. It only applies if you don't sign a new lease or move out.