A Perth landlady who illegally changed the locks and carried out renovations of a sick elderly tenants home while she was in hospital has been forced to pay almost $12,000 in fines and court costs.

Marlene Ruzica Pavlovich was found guilty in the Fremantle Magistrates court on June 30 for breaching two offences under the Residential Tenancies Act, which included entering a rental home in North Fremantle without a court order and changing the locks without any reasonable excuse.

Jan Wilson had rented the property since 1985.

The former real estate sales rep from Munster was fined $3000 and ordered to pay $8907 in court costs.

The court heard in February 2015, Ms Pavlovich organised prospective buyers to view the home despite not getting consent from the 87-year-old female tenant Jan Wilson, who was ill in hospital, or the renter's power of attorney who was at work.