A 47-year-old Nollamara woman has admitted trying to kill her foster brother's wife by setting her alight.

Debra Rosina Hughes this morning appeared in the Stirling Gardens Magistrate's Court via a video link from Bandyup Prison and pleaded guilty to the attempted murder on May 14.

She also admitted breaking in to her foster brother's Nollamara home as part of the crime and causing criminal damage by fire, with the court told the arson caused $100,000 of damage to the Homeswest building.

Her female victim, who attended court this morning, said after the appearance she was relieved with the guilty plea.

Hughes' defence lawyer requested a psychological assessment and report for her client, who is due for sentence on September 1.

Hughes is also due to appear on September 9 on a charge of breaching a violence restraining order. She did not plead to the charge today.

PERTH CHRISTIANA JONES