Alex Smith of Hazelbrook performs in The Louisa Collins Story

It's not every day a grown-up actor gets to play a 10-year-old girl, let alone one giving evidence against her mother - the last woman hanged for murder in NSW. Add to that the drama of performing in a crypt, and you have a macabre experience.

But Alex Smith of Hazelbrook is relishing reprising the role of May, which she first played in 2018.

A Poison Crown: The Louisa Collins Story, tells the tale of Louisa Collins who after four separate trials was finally, but mysteriously, convicted in 1889 of the murders of her first and second husbands. It's one of two plays in Deadhouse: Tales from Sydney Morgue which runs from October 23 - November 30 and is performed in a crypt under St James' Church in Sydney.

"Isn't it awful [what happened to Louisa]," Smith tells the Gazette. "I couldn't believe what she went through with four trials and then finally being found guilty. Nowadays we've discovered new evidence, but we'll never know if she was guilty or innocent."

May gave some of the most important testimony at the trial of her mother, evidence that the family kept Rough On Rats (a deadly arsenic-based poison which was popular at the time due to the rat plague of the 1880s) in the house.

Smith said May fought for clemency from the government for her mother - the day before her hanging - but to no avail. There was media hysteria about the case and some now liken Louisa Collins' treatment as similar to the court of public opinion that beset Lindy Chamberlain. Louisa did not display adequate public bereavement and contrition over the deaths of her two husbands. The audience of this play get to make their own decision.

The twenty-one-year Mountains actress said having "quite a high pitched voice" and a young face worked in her favour for the child role.

Smith's real life character May went on to be adopted by another family, but Smith doesn't know what happened to the seven other living siblings.

The play is an immersive experience for the audience and the creepy crypt setting sets the mood.

"Half the work is done for us [being in the crypt]. I think people like that it is immersive and a true story ... audience members walk around with us and one audience member [each night] plays the jury," she said.

Smith is an ex-Faulconbridge Public, Springwood High and Nepean High performing arts graduate and has a Bachelor of Performance from the Australian Institute of Music - Dramatic Arts.

Her other acting highlights in her young career include Streetcar On A Hot Tin Menagerie (Improv Theatre Sydney, 2019) and Eating Pomegranates (2019) at Wentworth Falls School of Arts.