Here's the RTB info on rent reviews outside a Rent Pressure Zone
, and Citizens Information has more details here
. She should politely inform the landlord that he's not permitted to conduct a rent review until 24 months after the date she started her tenancy; at that time, the landlord can review her rent and can send her a notice of a rent increase to take effect 90 days from the date of the notice. The rent increase can only be to "market rent" and in the notice the landlord must provide three examples of similar properties to demonstrate that the new rent is comparable.
As she's been in the property for more than six months and her tenancy started after December 2016, she has security of tenancy for six years under Part 4 of the Residential Tenancies Act
, meaning that the landlord cannot end her tenancy during that time unless he is selling the property, moving himself or a family member into it, or performing substantial renovations that would require vacant possession, so she doesn't need to worry that he will decide to kick her out if she pushes back on his illegal rent review. I'd still suggest being polite about it to try to maintain a cordial relationship with the landlord if possible, but he has no legal leg to stand on and she should be firm about her rights. If she needs assistance, she can contact Threshold
, an Irish charity who provide assistance on housing matters, and they should be able to offer her some support and advice on how to deal with her landlord.