If Ivy has notified the landlord of the repair (as Ivy has done) and the repair hasn't been done in a reasonable time (which it hasn't been), then the landlord has breached her tenancy agreement. Whether or not it is the strata corps fault doesn't change the landlord's obligations to Ivy.
If the landlord won't agree to the ongoing rent reduction, Ivy can do the following (after getting advice from the Tenants' Union or her local Tenants' Advice Service).
1. Ivy can make an application to the Consumer, Trader & Tenancy Tribunal claiming that the landlord has breached the tenancy agreement by failing to do the repair
2. Ivy can ask the Tribunal for orders requiring the landlord to make the repair by a specific date.
3. Ivy can also ask the Tribunal for compensation for any losses that she has suffered as a result of the landlord's failure to repair.
4. And finally, Ivy can ask the Tribunal to reduce her rent.
Ivy could send a letter to the landlord, letting them know that she intends to make the application and see if the landlord is more willing to negotiate.
I don't think that Ivy is more secure on the periodic agreement, under her fixed term the landlord couldn't terminate the agreement, unless Ivy actually breached the agreement (or when the fixed term came to an end).
However, although the landlord can now issue Ivy with a 90-day 'no grounds' termination, she does still have some security. A 'no grounds' notice cannot be issued in retaliation for Ivy trying to enforce her rights (such as by asking for a rent reduction or lodging a Tribunal application).
If Ivy were to receive such a notice, she should immediately contact the Tenants' Union or her local Tenants' Advice Service for advice.