The notice period in the landlord's lease is illegal.
Section 69 of the Residential Tenancies Act 2004 specifies:
(2) Such an agreement to a lesser period of notice being given
may only be entered into at, or after, the time it is indicated to the tenant or landlord (as appropriate) by the other party that he or she intends to terminate the tenancy.
(3) For the avoidance of doubt, a term of a lease or tenancy agreement cannot constitute such an agreement.
In other words, the landlord can agree a shorter notice period with a tenant at the end of a period of tenancy but not in the lease. The solicitor should have pointed this out to the landlord.
The same act specifies rent payments are considered late for the purposes of the law when they are paid more than 14 days after the landlord issues a written reminder.
The thread title tells us the rent has been late 'numerous times' when it appears from the solicitor's letter that the rent was late on two occasions and that there were no written reminders or 14 days of grace.
The landlord makes reference to becoming a tougher person and acting in a more businesslike fashion. the implication here is that to succeed in business she must make some kind of faustian deal and abandon her humanity for the sake of profits. This is a naive view of business. Being fair with people and learning from mistakes is a more profitable policy than bullying and illegality.
The questions about who should cut the grass, maintain appliances, pay for breakages and should be detailed in the lease agreement. Any omission like this can lead to dispute and misunderstanding. As the landlord drew up the agreement, it would be fair to either split the costs or favour the person who did not word the agreement - the tenant.
In business in Ireland, clients who pays bills within 14 days of the due date are not considered late. A business wouldn't have any customers if it came down too heavily on this behaviour. Yes writing reminder letters is a pain but this is part of business and just a task to carry out dispassionately every monday morning. Legal route is the last resort as it is aggressive and may cause the loss of a customer, as happened to the landlord in this case.
Perhaps the landlord should treat the tenant in the way that the landlord would want to be treated?
In this case, perhaps the landlord should consider if she would be happy if her bank attempted to repossess her house following three late mortgage payments on foot of an illegal clause in her mortgage agreement.